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Author SHA1 Message Date
Ming Ling
6afcf8ef0c mm, compaction: fix NR_ISOLATED_* stats for pfn based migration 
Since commit bda807d444 ("mm: migrate: support non-lru movable page
migration") isolate_migratepages_block) can isolate !PageLRU pages which
would acct_isolated account as NR_ISOLATED_*.  Accounting these non-lru
pages NR_ISOLATED_{ANON,FILE} doesn't make any sense and it can misguide
heuristics based on those counters such as pgdat_reclaimable_pages resp.
too_many_isolated which would lead to unexpected stalls during the
direct reclaim without any good reason.  Note that
__alloc_contig_migrate_range can isolate a lot of pages at once.

On mobile devices such as 512M ram android Phone, it may use a big zram
swap.  In some cases zram(zsmalloc) uses too many non-lru but
migratedable pages, such as:

      MemTotal: 468148 kB
      Normal free:5620kB
      Free swap:4736kB
      Total swap:409596kB
      ZRAM: 164616kB(zsmalloc non-lru pages)
      active_anon:60700kB
      inactive_anon:60744kB
      active_file:34420kB
      inactive_file:37532kB

Fix this by only accounting lru pages to NR_ISOLATED_* in
isolate_migratepages_block right after they were isolated and we still
know they were on LRU.  Drop acct_isolated because it is called after
the fact and we've lost that information.  Batching per-cpu counter
doesn't make much improvement anyway.  Also make sure that we uncharge
only LRU pages when putting them back on the LRU in
putback_movable_pages resp.  when unmap_and_move migrates the page.

[mhocko@suse.com: replace acct_isolated() with direct counting]
Fixes: bda807d444 ("mm: migrate: support non-lru movable page migration")
Link: http://lkml.kernel.org/r/20161019080240.9682-1-mhocko@kernel.org
Signed-off-by: Ming Ling <ming.ling@spreadtrum.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <js1304@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-12-12 18:55:07 -08:00
Vlastimil Babka
2031142028 mm, compaction: restrict fragindex to costly orders 
Fragmentation index and the vm.extfrag_threshold sysctl is meant as a
heuristic to prevent excessive compaction for costly orders (i.e.  THP).
It's unlikely to make any difference for non-costly orders, especially
with the default threshold.  But we cannot afford any uncertainty for
the non-costly orders where the only alternative to successful
reclaim/compaction is OOM.  After the recent patches we are guaranteed
maximum effort without heuristics from compaction before deciding OOM,
and fragindex is the last remaining heuristic.  Therefore skip fragindex
altogether for non-costly orders.

Suggested-by: Michal Hocko <mhocko@suse.com>
Link: http://lkml.kernel.org/r/20160926162025.21555-5-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:29 -07:00
Vlastimil Babka
cc5c9f098f mm, compaction: ignore fragindex from compaction_zonelist_suitable() 
The compaction_zonelist_suitable() function tries to determine if
compaction will be able to proceed after sufficient reclaim, i.e.
whether there are enough reclaimable pages to provide enough order-0
freepages for compaction.

This addition of reclaimable pages to the free pages works well for the
order-0 watermark check, but in the fragmentation index check we only
consider truly free pages.  Thus we can get fragindex value close to 0
which indicates failure do to lack of memory, and wrongly decide that
compaction won't be suitable even after reclaim.

Instead of trying to somehow adjust fragindex for reclaimable pages,
let's just skip it from compaction_zonelist_suitable().

Link: http://lkml.kernel.org/r/20160926162025.21555-4-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:29 -07:00
Vlastimil Babka
9f7e338793 mm, compaction: make full priority ignore pageblock suitability 
Several people have reported premature OOMs for order-2 allocations
(stack) due to OOM rework in 4.7.  In the scenario (parallel kernel
build and dd writing to two drives) many pageblocks get marked as
Unmovable and compaction free scanner struggles to isolate free pages.
Joonsoo Kim pointed out that the free scanner skips pageblocks that are
not movable to prevent filling them and forcing non-movable allocations
to fallback to other pageblocks.  Such heuristic makes sense to help
prevent long-term fragmentation, but premature OOMs are relatively more
urgent problem.  As a compromise, this patch disables the heuristic only
for the ultimate compaction priority.

Link: http://lkml.kernel.org/r/20160906135258.18335-5-vbabka@suse.cz
Reported-by: Ralf-Peter Rohbeck <Ralf-Peter.Rohbeck@quantum.com>
Reported-by: Arkadiusz Miskiewicz <a.miskiewicz@gmail.com>
Reported-by: Olaf Hering <olaf@aepfle.de>
Suggested-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:29 -07:00
Vlastimil Babka
8348faf91f mm, compaction: require only min watermarks for non-costly orders 
The __compaction_suitable() function checks the low watermark plus a
compact_gap() gap to decide if there's enough free memory to perform
compaction.  Then __isolate_free_page uses low watermark check to decide
if particular free page can be isolated.  In the latter case, using low
watermark is needlessly pessimistic, as the free page isolations are
only temporary.  For __compaction_suitable() the higher watermark makes
sense for high-order allocations where more freepages increase the
chance of success, and we can typically fail with some order-0 fallback
when the system is struggling to reach that watermark.  But for
low-order allocation, forming the page should not be that hard.  So
using low watermark here might just prevent compaction from even trying,
and eventually lead to OOM killer even if we are above min watermarks.

So after this patch, we use min watermark for non-costly orders in
__compaction_suitable(), and for all orders in __isolate_free_page().

[vbabka@suse.cz: clarify __isolate_free_page() comment]
 Link: http://lkml.kernel.org/r/7ae4baec-4eca-e70b-2a69-94bea4fb19fa@suse.cz
Link: http://lkml.kernel.org/r/20160810091226.6709-11-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:27 -07:00
Vlastimil Babka
984fdba6a3 mm, compaction: use proper alloc_flags in __compaction_suitable() 
The __compaction_suitable() function checks the low watermark plus a
compact_gap() gap to decide if there's enough free memory to perform
compaction.  This check uses direct compactor's alloc_flags, but that's
wrong, since these flags are not applicable for freepage isolation.

For example, alloc_flags may indicate access to memory reserves, making
compaction proceed, and then fail watermark check during the isolation.

A similar problem exists for ALLOC_CMA, which may be part of
alloc_flags, but not during freepage isolation.  In this case however it
makes sense to use ALLOC_CMA both in __compaction_suitable() and
__isolate_free_page(), since there's actually nothing preventing the
freepage scanner to isolate from CMA pageblocks, with the assumption
that a page that could be migrated once by compaction can be migrated
also later by CMA allocation.  Thus we should count pages in CMA
pageblocks when considering compaction suitability and when isolating
freepages.

To sum up, this patch should remove some false positives from
__compaction_suitable(), and allow compaction to proceed when free pages
required for compaction reside in the CMA pageblocks.

Link: http://lkml.kernel.org/r/20160810091226.6709-10-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:27 -07:00
Vlastimil Babka
9861a62c33 mm, compaction: create compact_gap wrapper 
Compaction uses a watermark gap of (2UL << order) pages at various
places and it's not immediately obvious why.  Abstract it through a
compact_gap() wrapper to create a single place with a thorough
explanation.

[vbabka@suse.cz: clarify the comment of compact_gap()]
 Link: http://lkml.kernel.org/r/7b6aed1f-fdf8-2063-9ff4-bbe4de712d37@suse.cz
Link: http://lkml.kernel.org/r/20160810091226.6709-9-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:27 -07:00
Vlastimil Babka
f2b8228c5f mm, compaction: use correct watermark when checking compaction success 
The __compact_finished() function uses low watermark in a check that has
to pass if the direct compaction is to finish and allocation should
succeed.  This is too pessimistic, as the allocation will typically use
min watermark.  It may happen that during compaction, we drop below the
low watermark (due to parallel activity), but still form the target
high-order page.  By checking against low watermark, we might needlessly
continue compaction.

Similarly, __compaction_suitable() uses low watermark in a check whether
allocation can succeed without compaction.  Again, this is unnecessarily
pessimistic.

After this patch, these check will use direct compactor's alloc_flags to
determine the watermark, which is effectively the min watermark.

Link: http://lkml.kernel.org/r/20160810091226.6709-8-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:27 -07:00
Vlastimil Babka
a8e025e55b mm, compaction: add the ultimate direct compaction priority 
During reclaim/compaction loop, it's desirable to get a final answer
from unsuccessful compaction so we can either fail the allocation or
invoke the OOM killer.  However, heuristics such as deferred compaction
or pageblock skip bits can cause compaction to skip parts or whole zones
and lead to premature OOM's, failures or excessive reclaim/compaction
retries.

To remedy this, we introduce a new direct compaction priority called
COMPACT_PRIO_SYNC_FULL, which instructs direct compaction to:

 - ignore deferred compaction status for a zone
 - ignore pageblock skip hints
 - ignore cached scanner positions and scan the whole zone

The new priority should get eventually picked up by
should_compact_retry() and this should improve success rates for costly
allocations using __GFP_REPEAT, such as hugetlbfs allocations, and
reduce some corner-case OOM's for non-costly allocations.

Link: http://lkml.kernel.org/r/20160810091226.6709-6-vbabka@suse.cz
[vbabka@suse.cz: use the MIN_COMPACT_PRIORITY alias]
  Link: http://lkml.kernel.org/r/d443b884-87e7-1c93-8684-3a3a35759fb1@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:27 -07:00
Vlastimil Babka
7ceb009a22 mm, compaction: don't recheck watermarks after COMPACT_SUCCESS 
Joonsoo has reminded me that in a later patch changing watermark checks
throughout compaction I forgot to update checks in
try_to_compact_pages() and compactd_do_work().  Closer inspection
however shows that they are redundant now in the success case, because
compact_zone() now reliably reports this with COMPACT_SUCCESS.  So
effectively the checks just repeat (a subset) of checks that have just
passed.  So instead of checking watermarks again, just test the return
value.

Note it's also possible that compaction would declare failure e.g.
because its find_suitable_fallback() is more strict than simple
watermark check, and then the watermark check we are removing would then
still succeed.  After this patch this is not possible and it's arguably
better, because for long-term fragmentation avoidance we should rather
try a different zone than allocate with the unsuitable fallback.  If
compaction of all zones fail and the allocation is important enough, it
will retry and succeed anyway.

Also remove the stray "bool success" variable from kcompactd_do_work().

Link: http://lkml.kernel.org/r/20160810091226.6709-5-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:27 -07:00
Vlastimil Babka
cf378319d3 mm, compaction: rename COMPACT_PARTIAL to COMPACT_SUCCESS 
COMPACT_PARTIAL has historically meant that compaction returned after
doing some work without fully compacting a zone.  It however didn't
distinguish if compaction terminated because it succeeded in creating
the requested high-order page.  This has changed recently and now we
only return COMPACT_PARTIAL when compaction thinks it succeeded, or the
high-order watermark check in compaction_suitable() passes and no
compaction needs to be done.

So at this point we can make the return value clearer by renaming it to
COMPACT_SUCCESS.  The next patch will remove some redundant tests for
success where compaction just returned COMPACT_SUCCESS.

Link: http://lkml.kernel.org/r/20160810091226.6709-4-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:27 -07:00
Vlastimil Babka
791cae9620 mm, compaction: cleanup unused functions 
Since kswapd compaction moved to kcompactd, compact_pgdat() is not
called anymore, so we remove it.  The only caller of __compact_pgdat()
is compact_node(), so we merge them and remove code that was only
reachable from kswapd.

Link: http://lkml.kernel.org/r/20160810091226.6709-3-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:27 -07:00
Vlastimil Babka
06ed29989f mm, compaction: make whole_zone flag ignore cached scanner positions 
Patch series "make direct compaction more deterministic")

This is mostly a followup to Michal's oom detection rework, which
highlighted the need for direct compaction to provide better feedback in
reclaim/compaction loop, so that it can reliably recognize when
compaction cannot make further progress, and allocation should invoke
OOM killer or fail.  We've discussed this at LSF/MM [1] where I proposed
expanding the async/sync migration mode used in compaction to more
general "priorities".  This patchset adds one new priority that just
overrides all the heuristics and makes compaction fully scan all zones.
I don't currently think that we need more fine-grained priorities, but
we'll see.  Other than that there's some smaller fixes and cleanups,
mainly related to the THP-specific hacks.

I've tested this with stress-highalloc in GFP_KERNEL order-4 and
THP-like order-9 scenarios.  There's some improvement for compaction
stats for the order-4, which is likely due to the better watermarks
handling.  In the previous version I reported mostly noise wrt
compaction stats, and decreased direct reclaim - now the reclaim is
without difference.  I believe this is due to the less aggressive
compaction priority increase in patch 6.

"before" is a mmotm tree prior to 4.7 release plus the first part of the
series that was sent and merged separately

                                    before        after
order-4:

Compaction stalls                    27216       30759
Compaction success                   19598       25475
Compaction failures                   7617        5283
Page migrate success                370510      464919
Page migrate failure                 25712       27987
Compaction pages isolated           849601     1041581
Compaction migrate scanned       143146541   101084990
Compaction free scanned          208355124   144863510
Compaction cost                       1403        1210

order-9:

Compaction stalls                     7311        7401
Compaction success                    1634        1683
Compaction failures                   5677        5718
Page migrate success                194657      183988
Page migrate failure                  4753        4170
Compaction pages isolated           498790      456130
Compaction migrate scanned          565371      524174
Compaction free scanned            4230296     4250744
Compaction cost                        215         203

[1] https://lwn.net/Articles/684611/

This patch (of 11):

A recent patch has added whole_zone flag that compaction sets when
scanning starts from the zone boundary, in order to report that zone has
been fully scanned in one attempt.  For allocations that want to try
really hard or cannot fail, we will want to introduce a mode where
scanning whole zone is guaranteed regardless of the cached positions.

This patch reuses the whole_zone flag in a way that if it's already
passed true to compaction, the cached scanner positions are ignored.
Employing this flag during reclaim/compaction loop will be done in the
next patch.  This patch however converts compaction invoked from
userspace via procfs to use this flag.  Before this patch, the cached
positions were first reset to zone boundaries and then read back from
struct zone, so there was a window where a parallel compaction could
replace the reset values, making the manual compaction less effective.
Using the flag instead of performing reset is more robust.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20160810091226.6709-2-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-10-07 18:46:27 -07:00
Vlastimil Babka
c3486f5376 mm, compaction: simplify contended compaction handling 
Async compaction detects contention either due to failing trylock on
zone->lock or lru_lock, or by need_resched().  Since 1f9efdef4f ("mm,
compaction: khugepaged should not give up due to need_resched()") the
code got quite complicated to distinguish these two up to the
__alloc_pages_slowpath() level, so different decisions could be taken
for khugepaged allocations.

After the recent changes, khugepaged allocations don't check for
contended compaction anymore, so we again don't need to distinguish lock
and sched contention, and simplify the current convoluted code a lot.

However, I believe it's also possible to simplify even more and
completely remove the check for contended compaction after the initial
async compaction for costly orders, which was originally aimed at THP
page fault allocations.  There are several reasons why this can be done
now:

- with the new defaults, THP page faults no longer do reclaim/compaction at
  all, unless the system admin has overridden the default, or application has
  indicated via madvise that it can benefit from THP's. In both cases, it
  means that the potential extra latency is expected and worth the benefits.
- even if reclaim/compaction proceeds after this patch where it previously
  wouldn't, the second compaction attempt is still async and will detect the
  contention and back off, if the contention persists
- there are still heuristics like deferred compaction and pageblock skip bits
  in place that prevent excessive THP page fault latencies

Link: http://lkml.kernel.org/r/20160721073614.24395-9-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-28 16:07:41 -07:00
Vlastimil Babka
a5508cd83f mm, compaction: introduce direct compaction priority 
In the context of direct compaction, for some types of allocations we
would like the compaction to either succeed or definitely fail while
trying as hard as possible.  Current async/sync_light migration mode is
insufficient, as there are heuristics such as caching scanner positions,
marking pageblocks as unsuitable or deferring compaction for a zone.  At
least the final compaction attempt should be able to override these
heuristics.

To communicate how hard compaction should try, we replace migration mode
with a new enum compact_priority and change the relevant function
signatures.  In compact_zone_order() where struct compact_control is
constructed, the priority is mapped to suitable control flags.  This
patch itself has no functional change, as the current priority levels
are mapped back to the same migration modes as before.  Expanding them
will be done next.

Note that !CONFIG_COMPACTION variant of try_to_compact_pages() is
removed, as the only caller exists under CONFIG_COMPACTION.

Link: http://lkml.kernel.org/r/20160721073614.24395-8-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-28 16:07:41 -07:00
Hugh Dickins
1d2047fefa mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode 
At present MIGRATE_SYNC_LIGHT is allowing __isolate_lru_page() to
isolate a PageWriteback page, which __unmap_and_move() then rejects with
-EBUSY: of course the writeback might complete in between, but that's
not what we usually expect, so probably better not to isolate it.

When tested by stress-highalloc from mmtests, this has reduced the
number of page migrate failures by 60-70%.

Link: http://lkml.kernel.org/r/20160721073614.24395-2-vbabka@suse.cz
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-28 16:07:41 -07:00
Mel Gorman
5a1c84b404 mm: remove reclaim and compaction retry approximations 
If per-zone LRU accounting is available then there is no point
approximating whether reclaim and compaction should retry based on pgdat
statistics.  This is effectively a revert of "mm, vmstat: remove zone
and node double accounting by approximating retries" with the difference
that inactive/active stats are still available.  This preserves the
history of why the approximation was retried and why it had to be
reverted to handle OOM kills on 32-bit systems.

Link: http://lkml.kernel.org/r/1469110261-7365-4-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-28 16:07:41 -07:00
Mel Gorman
bca6759258 mm, vmstat: remove zone and node double accounting by approximating retries 
The number of LRU pages, dirty pages and writeback pages must be
accounted for on both zones and nodes because of the reclaim retry
logic, compaction retry logic and highmem calculations all depending on
per-zone stats.

Many lowmem allocations are immune from OOM kill due to a check in
__alloc_pages_may_oom for (ac->high_zoneidx < ZONE_NORMAL) since commit
03668b3ceb ("oom: avoid oom killer for lowmem allocations").  The
exception is costly high-order allocations or allocations that cannot
fail.  If the __alloc_pages_may_oom avoids OOM-kill for low-order lowmem
allocations then it would fall through to __alloc_pages_direct_compact.

This patch will blindly retry reclaim for zone-constrained allocations
in should_reclaim_retry up to MAX_RECLAIM_RETRIES.  This is not ideal
but without per-zone stats there are not many alternatives.  The impact
it that zone-constrained allocations may delay before considering the
OOM killer.

As there is no guarantee enough memory can ever be freed to satisfy
compaction, this patch avoids retrying compaction for zone-contrained
allocations.

In combination, that means that the per-node stats can be used when
deciding whether to continue reclaim using a rough approximation.  While
it is possible this will make the wrong decision on occasion, it will
not infinite loop as the number of reclaim attempts is capped by
MAX_RECLAIM_RETRIES.

The final step is calculating the number of dirtyable highmem pages.  As
those calculations only care about the global count of file pages in
highmem.  This patch uses a global counter used instead of per-zone
stats as it is sufficient.

In combination, this allows the per-zone LRU and dirty state counters to
be removed.

[mgorman@techsingularity.net: fix acct_highmem_file_pages()]
  Link: http://lkml.kernel.org/r/1468853426-12858-4-git-send-email-mgorman@techsingularity.netLink: http://lkml.kernel.org/r/1467970510-21195-35-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Suggested by: Michal Hocko <mhocko@kernel.org>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-28 16:07:41 -07:00
Mel Gorman
599d0c954f mm, vmscan: move LRU lists to node 
This moves the LRU lists from the zone to the node and related data such
as counters, tracing, congestion tracking and writeback tracking.

Unfortunately, due to reclaim and compaction retry logic, it is
necessary to account for the number of LRU pages on both zone and node
logic.  Most reclaim logic is based on the node counters but the retry
logic uses the zone counters which do not distinguish inactive and
active sizes.  It would be possible to leave the LRU counters on a
per-zone basis but it's a heavier calculation across multiple cache
lines that is much more frequent than the retry checks.

Other than the LRU counters, this is mostly a mechanical patch but note
that it introduces a number of anomalies.  For example, the scans are
per-zone but using per-node counters.  We also mark a node as congested
when a zone is congested.  This causes weird problems that are fixed
later but is easier to review.

In the event that there is excessive overhead on 32-bit systems due to
the nodes being on LRU then there are two potential solutions

1. Long-term isolation of highmem pages when reclaim is lowmem

   When pages are skipped, they are immediately added back onto the LRU
   list. If lowmem reclaim persisted for long periods of time, the same
   highmem pages get continually scanned. The idea would be that lowmem
   keeps those pages on a separate list until a reclaim for highmem pages
   arrives that splices the highmem pages back onto the LRU. It potentially
   could be implemented similar to the UNEVICTABLE list.

   That would reduce the skip rate with the potential corner case is that
   highmem pages have to be scanned and reclaimed to free lowmem slab pages.

2. Linear scan lowmem pages if the initial LRU shrink fails

   This will break LRU ordering but may be preferable and faster during
   memory pressure than skipping LRU pages.

Link: http://lkml.kernel.org/r/1467970510-21195-4-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-28 16:07:41 -07:00
Mel Gorman
a52633d8e9 mm, vmscan: move lru_lock to the node 
Node-based reclaim requires node-based LRUs and locking.  This is a
preparation patch that just moves the lru_lock to the node so later
patches are easier to review.  It is a mechanical change but note this
patch makes contention worse because the LRU lock is hotter and direct
reclaim and kswapd can contend on the same lock even when reclaiming
from different zones.

Link: http://lkml.kernel.org/r/1467970510-21195-3-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-28 16:07:41 -07:00
Ganesh Mahendran
b2b331f966 mm/compaction: remove unnecessary order check in try_to_compact_pages() 
The caller __alloc_pages_direct_compact() already checked (order == 0)
so there's no need to check again.

Link: http://lkml.kernel.org/r/1465973568-3496-1-git-send-email-opensource.ganesh@gmail.com
Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-28 16:07:41 -07:00
Joonsoo Kim
46f24fd857 mm/page_alloc: introduce post allocation processing on page allocator 
This patch is motivated from Hugh and Vlastimil's concern [1].

There are two ways to get freepage from the allocator.  One is using
normal memory allocation API and the other is __isolate_free_page()
which is internally used for compaction and pageblock isolation.  Later
usage is rather tricky since it doesn't do whole post allocation
processing done by normal API.

One problematic thing I already know is that poisoned page would not be
checked if it is allocated by __isolate_free_page().  Perhaps, there
would be more.

We could add more debug logic for allocated page in the future and this
separation would cause more problem.  I'd like to fix this situation at
this time.  Solution is simple.  This patch commonize some logic for
newly allocated page and uses it on all sites.  This will solve the
problem.

[1] http://marc.info/?i=alpine.LSU.2.11.1604270029350.7066%40eggly.anvils%3E

[iamjoonsoo.kim@lge.com: mm-page_alloc-introduce-post-allocation-processing-on-page-allocator-v3]
  Link: http://lkml.kernel.org/r/1464230275-25791-7-git-send-email-iamjoonsoo.kim@lge.com
  Link: http://lkml.kernel.org/r/1466150259-27727-9-git-send-email-iamjoonsoo.kim@lge.com
Link: http://lkml.kernel.org/r/1464230275-25791-7-git-send-email-iamjoonsoo.kim@lge.com
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-26 16:19:19 -07:00
Joonsoo Kim
83358ece26 mm/page_owner: initialize page owner without holding the zone lock 
It's not necessary to initialized page_owner with holding the zone lock.
It would cause more contention on the zone lock although it's not a big
problem since it is just debug feature.  But, it is better than before
so do it.  This is also preparation step to use stackdepot in page owner
feature.  Stackdepot allocates new pages when there is no reserved space
and holding the zone lock in this case will cause deadlock.

Link: http://lkml.kernel.org/r/1464230275-25791-2-git-send-email-iamjoonsoo.kim@lge.com
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-26 16:19:19 -07:00
Joonsoo Kim
66c64223ad mm/compaction: split freepages without holding the zone lock 
We don't need to split freepages with holding the zone lock.  It will
cause more contention on zone lock so not desirable.

[rientjes@google.com: if __isolate_free_page() fails, avoid adding to freelist so we don't call map_pages() with it]
  Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1606211447001.43430@chino.kir.corp.google.com
Link: http://lkml.kernel.org/r/1464230275-25791-1-git-send-email-iamjoonsoo.kim@lge.com
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-26 16:19:19 -07:00
Minchan Kim
3783689a1a zsmalloc: introduce zspage structure 
We have squeezed meta data of zspage into first page's descriptor.  So,
to get meta data from subpage, we should get first page first of all.
But it makes trouble to implment page migration feature of zsmalloc
because any place where to get first page from subpage can be raced with
first page migration.  IOW, first page it got could be stale.  For
preventing it, I have tried several approahces but it made code
complicated so finally, I concluded to separate metadata from first
page.  Of course, it consumes more memory.  IOW, 16bytes per zspage on
32bit at the moment.  It means we lost 1% at *worst case*(40B/4096B)
which is not bad I think at the cost of maintenance.

Link: http://lkml.kernel.org/r/1464736881-24886-9-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-26 16:19:19 -07:00
Minchan Kim
b1123ea6d3 mm: balloon: use general non-lru movable page feature 
Now, VM has a feature to migrate non-lru movable pages so balloon
doesn't need custom migration hooks in migrate.c and compaction.c.

Instead, this patch implements the page->mapping->a_ops->
{isolate|migrate|putback} functions.

With that, we could remove hooks for ballooning in general migration
functions and make balloon compaction simple.

[akpm@linux-foundation.org: compaction.h requires that the includer first include node.h]
Link: http://lkml.kernel.org/r/1464736881-24886-4-git-send-email-minchan@kernel.org
Signed-off-by: Gioh Kim <gi-oh.kim@profitbricks.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-26 16:19:19 -07:00
Minchan Kim
bda807d444 mm: migrate: support non-lru movable page migration 
We have allowed migration for only LRU pages until now and it was enough
to make high-order pages.  But recently, embedded system(e.g., webOS,
android) uses lots of non-movable pages(e.g., zram, GPU memory) so we
have seen several reports about troubles of small high-order allocation.
For fixing the problem, there were several efforts (e,g,.  enhance
compaction algorithm, SLUB fallback to 0-order page, reserved memory,
vmalloc and so on) but if there are lots of non-movable pages in system,
their solutions are void in the long run.

So, this patch is to support facility to change non-movable pages with
movable.  For the feature, this patch introduces functions related to
migration to address_space_operations as well as some page flags.

If a driver want to make own pages movable, it should define three
functions which are function pointers of struct
address_space_operations.

1. bool (*isolate_page) (struct page *page, isolate_mode_t mode);

What VM expects on isolate_page function of driver is to return *true*
if driver isolates page successfully.  On returing true, VM marks the
page as PG_isolated so concurrent isolation in several CPUs skip the
page for isolation.  If a driver cannot isolate the page, it should
return *false*.

Once page is successfully isolated, VM uses page.lru fields so driver
shouldn't expect to preserve values in that fields.

2. int (*migratepage) (struct address_space *mapping,
		struct page *newpage, struct page *oldpage, enum migrate_mode);

After isolation, VM calls migratepage of driver with isolated page.  The
function of migratepage is to move content of the old page to new page
and set up fields of struct page newpage.  Keep in mind that you should
indicate to the VM the oldpage is no longer movable via
__ClearPageMovable() under page_lock if you migrated the oldpage
successfully and returns 0.  If driver cannot migrate the page at the
moment, driver can return -EAGAIN.  On -EAGAIN, VM will retry page
migration in a short time because VM interprets -EAGAIN as "temporal
migration failure".  On returning any error except -EAGAIN, VM will give
up the page migration without retrying in this time.

Driver shouldn't touch page.lru field VM using in the functions.

3. void (*putback_page)(struct page *);

If migration fails on isolated page, VM should return the isolated page
to the driver so VM calls driver's putback_page with migration failed
page.  In this function, driver should put the isolated page back to the
own data structure.

4. non-lru movable page flags

There are two page flags for supporting non-lru movable page.

* PG_movable

Driver should use the below function to make page movable under
page_lock.

	void __SetPageMovable(struct page *page, struct address_space *mapping)

It needs argument of address_space for registering migration family
functions which will be called by VM.  Exactly speaking, PG_movable is
not a real flag of struct page.  Rather than, VM reuses page->mapping's
lower bits to represent it.

	#define PAGE_MAPPING_MOVABLE 0x2
	page->mapping = page->mapping | PAGE_MAPPING_MOVABLE;

so driver shouldn't access page->mapping directly.  Instead, driver
should use page_mapping which mask off the low two bits of page->mapping
so it can get right struct address_space.

For testing of non-lru movable page, VM supports __PageMovable function.
However, it doesn't guarantee to identify non-lru movable page because
page->mapping field is unified with other variables in struct page.  As
well, if driver releases the page after isolation by VM, page->mapping
doesn't have stable value although it has PAGE_MAPPING_MOVABLE (Look at
__ClearPageMovable).  But __PageMovable is cheap to catch whether page
is LRU or non-lru movable once the page has been isolated.  Because LRU
pages never can have PAGE_MAPPING_MOVABLE in page->mapping.  It is also
good for just peeking to test non-lru movable pages before more
expensive checking with lock_page in pfn scanning to select victim.

For guaranteeing non-lru movable page, VM provides PageMovable function.
Unlike __PageMovable, PageMovable functions validates page->mapping and
mapping->a_ops->isolate_page under lock_page.  The lock_page prevents
sudden destroying of page->mapping.

Driver using __SetPageMovable should clear the flag via
__ClearMovablePage under page_lock before the releasing the page.

* PG_isolated

To prevent concurrent isolation among several CPUs, VM marks isolated
page as PG_isolated under lock_page.  So if a CPU encounters PG_isolated
non-lru movable page, it can skip it.  Driver doesn't need to manipulate
the flag because VM will set/clear it automatically.  Keep in mind that
if driver sees PG_isolated page, it means the page have been isolated by
VM so it shouldn't touch page.lru field.  PG_isolated is alias with
PG_reclaim flag so driver shouldn't use the flag for own purpose.

[opensource.ganesh@gmail.com: mm/compaction: remove local variable is_lru]
  Link: http://lkml.kernel.org/r/20160618014841.GA7422@leo-test
Link: http://lkml.kernel.org/r/1464736881-24886-3-git-send-email-minchan@kernel.org
Signed-off-by: Gioh Kim <gi-oh.kim@profitbricks.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: John Einar Reitan <john.reitan@foss.arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-26 16:19:19 -07:00
David Rientjes
a46cbf3bc5 mm, compaction: prevent VM_BUG_ON when terminating freeing scanner 
It's possible to isolate some freepages in a pageblock and then fail
split_free_page() due to the low watermark check.  In this case, we hit
VM_BUG_ON() because the freeing scanner terminated early without a
contended lock or enough freepages.

This should never have been a VM_BUG_ON() since it's not a fatal
condition.  It should have been a VM_WARN_ON() at best, or even handled
gracefully.

Regardless, we need to terminate anytime the full pageblock scan was not
done.  The logic belongs in isolate_freepages_block(), so handle its
state gracefully by terminating the pageblock loop and making a note to
restart at the same pageblock next time since it was not possible to
complete the scan this time.

[rientjes@google.com: don't rescan pages in a pageblock]
  Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1607111244150.83138@chino.kir.corp.google.com
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1606291436300.145590@chino.kir.corp.google.com
Signed-off-by: David Rientjes <rientjes@google.com>
Reported-by: Minchan Kim <minchan@kernel.org>
Tested-by: Minchan Kim <minchan@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-07-15 14:54:27 +09:00
David Rientjes
a4f04f2c69 mm, compaction: abort free scanner if split fails 
If the memory compaction free scanner cannot successfully split a free
page (only possible due to per-zone low watermark), terminate the free
scanner rather than continuing to scan memory needlessly.  If the
watermark is insufficient for a free page of order <= cc->order, then
terminate the scanner since all future splits will also likely fail.

This prevents the compaction freeing scanner from scanning all memory on
very large zones (very noticeable for zones > 128GB, for instance) when
all splits will likely fail while holding zone->lock.

compaction_alloc() iterating a 128GB zone has been benchmarked to take
over 400ms on some systems whereas any free page isolated and ready to
be split ends up failing in split_free_page() because of the low
watermark check and thus the iteration continues.

The next time compaction occurs, the freeing scanner will likely start
at the end of the zone again since no success was made previously and we
get the same lengthy iteration until the zone is brought above the low
watermark.  All thp page faults can take >400ms in such a state without
this fix.

Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1606211820350.97086@chino.kir.corp.google.com
Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-06-24 17:23:52 -07:00
Chen Feng
6cd9dc3e75 mm/compaction.c: fix zoneindex in kcompactd() 
While testing the kcompactd in my platform 3G MEM only DMA ZONE.  I
found the kcompactd never wakeup.  It seems the zoneindex has already
minus 1 before.  So the traverse here should be <=.

It fixes a regression where kswapd could previously compact, but
kcompactd not.  Not a crash fix though.

[akpm@linux-foundation.org: fix kcompactd_do_work() as well, per Hugh]
Link: http://lkml.kernel.org/r/1463659121-84124-1-git-send-email-puck.chen@hisilicon.com
Fixes: accf62422b ("mm, kswapd: replace kswapd compaction with waking up kcompactd")
Signed-off-by: Chen Feng <puck.chen@hisilicon.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zhuangluan Su <suzhuangluan@hisilicon.com>
Cc: Yiping Xu <xuyiping@hisilicon.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-20 17:58:30 -07:00
Michal Hocko
86a294a81f mm, oom, compaction: prevent from should_compact_retry looping for ever for costly orders 
"mm: consider compaction feedback also for costly allocation" has
removed the upper bound for the reclaim/compaction retries based on the
number of reclaimed pages for costly orders.  While this is desirable
the patch did miss a mis interaction between reclaim, compaction and the
retry logic.  The direct reclaim tries to get zones over min watermark
while compaction backs off and returns COMPACT_SKIPPED when all zones
are below low watermark + 1<<order gap.  If we are getting really close
to OOM then __compaction_suitable can keep returning COMPACT_SKIPPED a
high order request (e.g.  hugetlb order-9) while the reclaim is not able
to release enough pages to get us over low watermark.  The reclaim is
still able to make some progress (usually trashing over few remaining
pages) so we are not able to break out from the loop.

I have seen this happening with the same test described in "mm: consider
compaction feedback also for costly allocation" on a swapless system.
The original problem got resolved by "vmscan: consider classzone_idx in
compaction_ready" but it shows how things might go wrong when we
approach the oom event horizont.

The reason why compaction requires being over low rather than min
watermark is not clear to me.  This check was there essentially since
56de7263fc ("mm: compaction: direct compact when a high-order
allocation fails").  It is clearly an implementation detail though and
we shouldn't pull it into the generic retry logic while we should be
able to cope with such eventuality.  The only place in
should_compact_retry where we retry without any upper bound is for
compaction_withdrawn() case.

Introduce compaction_zonelist_suitable function which checks the given
zonelist and returns true only if there is at least one zone which would
would unblock __compaction_suitable if more memory got reclaimed.  In
this implementation it checks __compaction_suitable with NR_FREE_PAGES
plus part of the reclaimable memory as the target for the watermark
check.  The reclaimable memory is reduced linearly by the allocation
order.  The idea is that we do not want to reclaim all the remaining
memory for a single allocation request just unblock
__compaction_suitable which doesn't guarantee we will make a further
progress.

The new helper is then used if compaction_withdrawn() feedback was
provided so we do not retry if there is no outlook for a further
progress.  !costly requests shouldn't be affected much - e.g.  order-2
pages would require to have at least 64kB on the reclaimable LRUs while
order-9 would need at least 32M which should be enough to not lock up.

[vbabka@suse.cz: fix classzone_idx vs. high_zoneidx usage in compaction_zonelist_suitable]
[akpm@linux-foundation.org: fix it for Mel's mm-page_alloc-remove-field-from-alloc_context.patch]
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-20 17:58:30 -07:00
Michal Hocko
c8f7de0bfa mm, compaction: distinguish between full and partial COMPACT_COMPLETE 
COMPACT_COMPLETE now means that compaction and free scanner met.  This
is not very useful information if somebody just wants to use this
feedback and make any decisions based on that.  The current caller might
be a poor guy who just happened to scan tiny portion of the zone and
that could be the reason no suitable pages were compacted.  Make sure we
distinguish the full and partial zone walks.

Consumers should treat COMPACT_PARTIAL_SKIPPED as a potential success
and be optimistic in retrying.

The existing users of COMPACT_COMPLETE are conservatively changed to use
COMPACT_PARTIAL_SKIPPED as well but some of them should be probably
reconsidered and only defer the compaction only for COMPACT_COMPLETE
with the new semantic.

This patch shouldn't introduce any functional changes.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-20 17:58:30 -07:00
Michal Hocko
1d4746d395 mm, compaction: distinguish COMPACT_DEFERRED from COMPACT_SKIPPED 
try_to_compact_pages() can currently return COMPACT_SKIPPED even when
the compaction is defered for some zone just because zone DMA is skipped
in 99% of cases due to watermark checks.  This makes COMPACT_DEFERRED
basically unusable for the page allocator as a feedback mechanism.

Make sure we distinguish those two states properly and switch their
ordering in the enum.  This would mean that the COMPACT_SKIPPED will be
returned only when all eligible zones are skipped.

As a result COMPACT_DEFERRED handling for THP in __alloc_pages_slowpath
will be more precise and we would bail out rather than reclaim.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-20 17:58:30 -07:00
Michal Hocko
c46649deae mm, compaction: cover all compaction mode in compact_zone 
The compiler is complaining after "mm, compaction: change COMPACT_
constants into enum"

  mm/compaction.c: In function `compact_zone':
  mm/compaction.c:1350:2: warning: enumeration value `COMPACT_DEFERRED' not handled in switch [-Wswitch]
    switch (ret) {
    ^
  mm/compaction.c:1350:2: warning: enumeration value `COMPACT_COMPLETE' not handled in switch [-Wswitch]
  mm/compaction.c:1350:2: warning: enumeration value `COMPACT_NO_SUITABLE_PAGE' not handled in switch [-Wswitch]
  mm/compaction.c:1350:2: warning: enumeration value `COMPACT_NOT_SUITABLE_ZONE' not handled in switch [-Wswitch]
  mm/compaction.c:1350:2: warning: enumeration value `COMPACT_CONTENDED' not handled in switch [-Wswitch]

compaction_suitable is allowed to return only COMPACT_PARTIAL,
COMPACT_SKIPPED and COMPACT_CONTINUE so other cases are simply
impossible.  Put a VM_BUG_ON to catch an impossible return value.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-20 17:58:30 -07:00
Michal Hocko
ea7ab982b6 mm, compaction: change COMPACT_ constants into enum 
Compaction code is doing weird dances between COMPACT_FOO -> int ->
unsigned long

But there doesn't seem to be any reason for that.  All functions which
return/use one of those constants are not expecting any other value so it
really makes sense to define an enum for them and make it clear that no
other values are expected.

This is a pure cleanup and shouldn't introduce any functional changes.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-20 17:58:30 -07:00
Mel Gorman
93ea9964d1 mm, page_alloc: remove field from alloc_context 
The classzone_idx can be inferred from preferred_zoneref so remove the
unnecessary field and save stack space.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-19 19:12:14 -07:00
Mel Gorman
c603844bdc mm, page_alloc: convert alloc_flags to unsigned 
alloc_flags is a bitmask of flags but it is signed which does not
necessarily generate the best code depending on the compiler.  Even
without an impact, it makes more sense that this be unsigned.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-19 19:12:14 -07:00
Vlastimil Babka
fdd048e12c mm, compaction: skip blocks where isolation fails in async direct compaction 
The goal of direct compaction is to quickly make a high-order page
available for the pending allocation.  Within an aligned block of pages
of desired order, a single allocated page that cannot be isolated for
migration means that the block cannot fully merge to a buddy page that
would satisfy the allocation request.  Therefore we can reduce the
allocation stall by skipping the rest of the block immediately on
isolation failure.  For async compaction, this also means a higher
chance of succeeding until it detects contention.

We however shouldn't completely sacrifice the second objective of
compaction, which is to reduce overal long-term memory fragmentation.
As a compromise, perform the eager skipping only in direct async
compaction, while sync compaction (including kcompactd) remains
thorough.

Testing was done using stress-highalloc from mmtests, configured for
order-4 GFP_KERNEL allocations:

                                 4.6-rc1               4.6-rc1
                                  before                 after
  Success 1 Min         24.00 (  0.00%)       27.00 (-12.50%)
  Success 1 Mean        30.20 (  0.00%)       31.60 ( -4.64%)
  Success 1 Max         37.00 (  0.00%)       35.00 (  5.41%)
  Success 2 Min         42.00 (  0.00%)       32.00 ( 23.81%)
  Success 2 Mean        44.00 (  0.00%)       44.80 ( -1.82%)
  Success 2 Max         48.00 (  0.00%)       52.00 ( -8.33%)
  Success 3 Min         91.00 (  0.00%)       92.00 ( -1.10%)
  Success 3 Mean        92.20 (  0.00%)       92.80 ( -0.65%)
  Success 3 Max         94.00 (  0.00%)       93.00 (  1.06%)

We can see that success rates are unaffected by the skipping.

                4.6-rc1     4.6-rc1
                 before       after
  User         2587.42     2566.53
  System        482.89      471.20
  Elapsed      1395.68     1382.00

Times are not so useful metric for this benchmark as main portion is the
interfering kernel builds, but results do hint at reduced system times.

                                      4.6-rc1     4.6-rc1
                                       before       after
  Direct pages scanned                163614      159608
  Kswapd pages scanned               2070139     2078790
  Kswapd pages reclaimed             2061707     2069757
  Direct pages reclaimed              163354      159505

Reduced direct reclaim was unintended, but could be explained by more
successful first attempt at (async) direct compaction, which is
attempted before the first reclaim attempt in __alloc_pages_slowpath().

  Compaction stalls                    33052       39853
  Compaction success                   12121       19773
  Compaction failures                  20931       20079

Compaction is indeed more successful, and thus less likely to get
deferred, so there are also more direct compaction stalls.

  Page migrate success               3781876     3326819
  Page migrate failure                 45817       41774
  Compaction pages isolated          7868232     6941457
  Compaction migrate scanned       168160492   127269354
  Compaction migrate prescanned            0           0
  Compaction free scanned         2522142582  2326342620
  Compaction free direct alloc             0           0
  Compaction free dir. all. miss           0           0
  Compaction cost                       5252        4476

The patch reduces migration scanned pages by 25% thanks to the eager
skipping.

[hughd@google.com: prevent nr_isolated_* from going negative]
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-19 19:12:14 -07:00
Vlastimil Babka
a34753d275 mm, compaction: reduce spurious pcplist drains 
Compaction drains the local pcplists each time migration scanner moves
away from a cc->order aligned block where it isolated pages for
migration, so that the pages freed by migrations can merge into higher
orders.

The detection is currently coarser than it could be.  The
cc->last_migrated_pfn variable should track the lowest pfn that was
isolated for migration.  But it is set to the pfn where
isolate_migratepages_block() starts scanning, which is typically the
first pfn of the pageblock.  There, the scanner might fail to isolate
several order-aligned blocks, and then isolate COMPACT_CLUSTER_MAX in
another block.  This would cause the pcplists drain to be performed,
although the scanner didn't yet finish the block where it isolated from.

This patch thus makes cc->last_migrated_pfn handling more accurate by
setting it to the pfn of an actually isolated page in
isolate_migratepages_block().  Although practical effects of this patch
are likely low, it arguably makes the intent of the code more obvious.
Also the next patch will make async direct compaction skip blocks more
aggressively, and draining pcplists due to skipped blocks is wasteful.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-19 19:12:14 -07:00
Vlastimil Babka
06b6640a39 mm, compaction: wrap calculating first and last pfn of pageblock 
Compaction code has accumulated numerous instances of manual
calculations of the first (inclusive) and last (exclusive) pfn of a
pageblock (or a smaller block of given order), given a pfn within the
pageblock.

Wrap these calculations by introducing pageblock_start_pfn(pfn) and
pageblock_end_pfn(pfn) macros.

[vbabka@suse.cz: fix crash in get_pfnblock_flags_mask() from isolate_freepages():]
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-19 19:12:14 -07:00
Vlastimil Babka
172400c69c mm: fix kcompactd hang during memory offlining 
Assume memory47 is the last online block left in node1.  This will hang:

  # echo offline > /sys/devices/system/node/node1/memory47/state

After a couple of minutes, the following pops up in dmesg:

  INFO: task bash:957 blocked for more than 120 seconds.
         Not tainted 4.6.0-rc6+ #6
  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  bash            D ffff8800b7adbaf8     0   957    951 0x00000000
  Call Trace:
    schedule+0x35/0x80
    schedule_timeout+0x1ac/0x270
    wait_for_completion+0xe1/0x120
    kthread_stop+0x4f/0x110
    kcompactd_stop+0x26/0x40
    __offline_pages.constprop.28+0x7e6/0x840
    offline_pages+0x11/0x20
    memory_block_action+0x73/0x1d0
    memory_subsys_offline+0x47/0x60
    device_offline+0x86/0xb0
    store_mem_state+0xda/0xf0
    dev_attr_store+0x18/0x30
    sysfs_kf_write+0x37/0x40
    kernfs_fop_write+0x11d/0x170
    __vfs_write+0x37/0x120
    vfs_write+0xa9/0x1a0
    SyS_write+0x55/0xc0
    entry_SYSCALL_64_fastpath+0x1a/0xa4

kcompactd is waiting for kcompactd_max_order > 0 when it's woken up to
actually exit.  Check kthread_should_stop() to break out of the wait.

Fixes: 698b1b306 ("mm, compaction: introduce kcompactd").
Reported-by: Reza Arbab <arbab@linux.vnet.ibm.com>
Tested-by: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-05 17:38:53 -07:00
Hugh Dickins
14af4a5e9b mm, cma: prevent nr_isolated_* counters from going negative 
/proc/sys/vm/stat_refresh warns nr_isolated_anon and nr_isolated_file go
increasingly negative under compaction: which would add delay when
should be none, or no delay when should delay.  The bug in compaction
was due to a recent mmotm patch, but much older instance of the bug was
also noticed in isolate_migratepages_range() which is used for CMA and
gigantic hugepage allocations.

The bug is caused by putback_movable_pages() in an error path
decrementing the isolated counters without them being previously
incremented by acct_isolated().  Fix isolate_migratepages_range() by
removing the error-path putback, thus reaching acct_isolated() with
migratepages still isolated, and leaving putback to caller like most
other places do.

Fixes: edc2ca6124 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()")
[vbabka@suse.cz: expanded the changelog]
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-05-05 17:38:53 -07:00
Vlastimil Babka
accf62422b mm, kswapd: replace kswapd compaction with waking up kcompactd 
Similarly to direct reclaim/compaction, kswapd attempts to combine
reclaim and compaction to attempt making memory allocation of given
order available.

The details differ from direct reclaim e.g. in having high watermark as
a goal.  The code involved in kswapd's reclaim/compaction decisions has
evolved to be quite complex.

Testing reveals that it doesn't actually work in at least one scenario,
and closer inspection suggests that it could be greatly simplified
without compromising on the goal (make high-order page available) or
efficiency (don't reclaim too much).  The simplification relieas of
doing all compaction in kcompactd, which is simply woken up when high
watermarks are reached by kswapd's reclaim.

The scenario where kswapd compaction doesn't work was found with mmtests
test stress-highalloc configured to attempt order-9 allocations without
direct reclaim, just waking up kswapd.  There was no compaction attempt
from kswapd during the whole test.  Some added instrumentation shows
what happens:

 - balance_pgdat() sets end_zone to Normal, as it's not balanced
 - reclaim is attempted on DMA zone, which sets nr_attempted to 99, but
   it cannot reclaim anything, so sc.nr_reclaimed is 0
 - for zones DMA32 and Normal, kswapd_shrink_zone uses testorder=0, so
   it merely checks if high watermarks were reached for base pages.
   This is true, so no reclaim is attempted.  For DMA, testorder=0
   wasn't used, as compaction_suitable() returned COMPACT_SKIPPED
 - even though the pgdat_needs_compaction flag wasn't set to false, no
   compaction happens due to the condition sc.nr_reclaimed >
   nr_attempted being false (as 0 < 99)
 - priority-- due to nr_reclaimed being 0, repeat until priority reaches
   0 pgdat_balanced() is false as only the small zone DMA appears
   balanced (curiously in that check, watermark appears OK and
   compaction_suitable() returns COMPACT_PARTIAL, because a lower
   classzone_idx is used there)

Now, even if it was decided that reclaim shouldn't be attempted on the
DMA zone, the scenario would be the same, as (sc.nr_reclaimed=0 >
nr_attempted=0) is also false.  The condition really should use >= as
the comment suggests.  Then there is a mismatch in the check for setting
pgdat_needs_compaction to false using low watermark, while the rest uses
high watermark, and who knows what other subtlety.  Hopefully this
demonstrates that this is unsustainable.

Luckily we can simplify this a lot.  The reclaim/compaction decisions
make sense for direct reclaim scenario, but in kswapd, our primary goal
is to reach high watermark in order-0 pages.  Afterwards we can attempt
compaction just once.  Unlike direct reclaim, we don't reclaim extra
pages (over the high watermark), the current code already disallows it
for good reasons.

After this patch, we simply wake up kcompactd to process the pgdat,
after we have either succeeded or failed to reach the high watermarks in
kswapd, which goes to sleep.  We pass kswapd's order and classzone_idx,
so kcompactd can apply the same criteria to determine which zones are
worth compacting.  Note that we use the classzone_idx from
wakeup_kswapd(), not balanced_classzone_idx which can include higher
zones that kswapd tried to balance too, but didn't consider them in
pgdat_balanced().

Since kswapd now cannot create high-order pages itself, we need to
adjust how it determines the zones to be balanced.  The key element here
is adding a "highorder" parameter to zone_balanced, which, when set to
false, makes it consider only order-0 watermark instead of the desired
higher order (this was done previously by kswapd_shrink_zone(), but not
elsewhere).  This false is passed for example in pgdat_balanced().
Importantly, wakeup_kswapd() uses true to make sure kswapd and thus
kcompactd are woken up for a high-order allocation failure.

The last thing is to decide what to do with pageblock_skip bitmap
handling.  Compaction maintains a pageblock_skip bitmap to record
pageblocks where isolation recently failed.  This bitmap can be reset by
three ways:

1) direct compaction is restarting after going through the full deferred cycle

2) kswapd goes to sleep, and some other direct compaction has previously
   finished scanning the whole zone and set zone->compact_blockskip_flush.
   Note that a successful direct compaction clears this flag.

3) compaction was invoked manually via trigger in /proc

The case 2) is somewhat fuzzy to begin with, but after introducing
kcompactd we should update it.  The check for direct compaction in 1),
and to set the flush flag in 2) use current_is_kswapd(), which doesn't
work for kcompactd.  Thus, this patch adds bool direct_compaction to
compact_control to use in 2).  For the case 1) we remove the check
completely - unlike the former kswapd compaction, kcompactd does use the
deferred compaction functionality, so flushing tied to restarting from
deferred compaction makes sense here.

Note that when kswapd goes to sleep, kcompactd is woken up, so it will
see the flushed pageblock_skip bits.  This is different from when the
former kswapd compaction observed the bits and I believe it makes more
sense.  Kcompactd can afford to be more thorough than a direct
compaction trying to limit allocation latency, or kswapd whose primary
goal is to reclaim.

For testing, I used stress-highalloc configured to do order-9
allocations with GFP_NOWAIT|__GFP_HIGH|__GFP_COMP, so they relied just
on kswapd/kcompactd reclaim/compaction (the interfering kernel builds in
phases 1 and 2 work as usual):

stress-highalloc
                        4.5-rc1+before          4.5-rc1+after
                             -nodirect              -nodirect
Success 1 Min          1.00 (  0.00%)         5.00 (-66.67%)
Success 1 Mean         1.40 (  0.00%)         6.20 (-55.00%)
Success 1 Max          2.00 (  0.00%)         7.00 (-16.67%)
Success 2 Min          1.00 (  0.00%)         5.00 (-66.67%)
Success 2 Mean         1.80 (  0.00%)         6.40 (-52.38%)
Success 2 Max          3.00 (  0.00%)         7.00 (-16.67%)
Success 3 Min         34.00 (  0.00%)        62.00 (  1.59%)
Success 3 Mean        41.80 (  0.00%)        63.80 (  1.24%)
Success 3 Max         53.00 (  0.00%)        65.00 (  2.99%)

User                          3166.67        3181.09
System                        1153.37        1158.25
Elapsed                       1768.53        1799.37

                            4.5-rc1+before   4.5-rc1+after
                                 -nodirect    -nodirect
Direct pages scanned                32938        32797
Kswapd pages scanned              2183166      2202613
Kswapd pages reclaimed            2152359      2143524
Direct pages reclaimed              32735        32545
Percentage direct scans                1%           1%
THP fault alloc                       579          612
THP collapse alloc                    304          316
THP splits                              0            0
THP fault fallback                    793          778
THP collapse fail                      11           16
Compaction stalls                    1013         1007
Compaction success                     92           67
Compaction failures                   920          939
Page migrate success               238457       721374
Page migrate failure                23021        23469
Compaction pages isolated          504695      1479924
Compaction migrate scanned         661390      8812554
Compaction free scanned          13476658     84327916
Compaction cost                       262          838

After this patch we see improvements in allocation success rate
(especially for phase 3) along with increased compaction activity.  The
compaction stalls (direct compaction) in the interfering kernel builds
(probably THP's) also decreased somewhat thanks to kcompactd activity,
yet THP alloc successes improved a bit.

Note that elapsed and user time isn't so useful for this benchmark,
because of the background interference being unpredictable.  It's just
to quickly spot some major unexpected differences.  System time is
somewhat more useful and that didn't increase.

Also (after adjusting mmtests' ftrace monitor):

Time kswapd awake               2547781     2269241
Time kcompactd awake                  0      119253
Time direct compacting           939937      557649
Time kswapd compacting                0           0
Time kcompactd compacting             0      119099

The decrease of overal time spent compacting appears to not match the
increased compaction stats.  I suspect the tasks get rescheduled and
since the ftrace monitor doesn't see that, the reported time is wall
time, not CPU time.  But arguably direct compactors care about overall
latency anyway, whether busy compacting or waiting for CPU doesn't
matter.  And that latency seems to almost halved.

It's also interesting how much time kswapd spent awake just going
through all the priorities and failing to even try compacting, over and
over.

We can also configure stress-highalloc to perform both direct
reclaim/compaction and wakeup kswapd/kcompactd, by using
GFP_KERNEL|__GFP_HIGH|__GFP_COMP:

stress-highalloc
                        4.5-rc1+before         4.5-rc1+after
                               -direct               -direct
Success 1 Min          4.00 (  0.00%)        9.00 (-50.00%)
Success 1 Mean         8.00 (  0.00%)       10.00 (-19.05%)
Success 1 Max         12.00 (  0.00%)       11.00 ( 15.38%)
Success 2 Min          4.00 (  0.00%)        9.00 (-50.00%)
Success 2 Mean         8.20 (  0.00%)       10.00 (-16.28%)
Success 2 Max         13.00 (  0.00%)       11.00 (  8.33%)
Success 3 Min         75.00 (  0.00%)       74.00 (  1.33%)
Success 3 Mean        75.60 (  0.00%)       75.20 (  0.53%)
Success 3 Max         77.00 (  0.00%)       76.00 (  0.00%)

User                          3344.73       3246.04
System                        1194.24       1172.29
Elapsed                       1838.04       1836.76

                            4.5-rc1+before  4.5-rc1+after
                                   -direct     -direct
Direct pages scanned               125146      120966
Kswapd pages scanned              2119757     2135012
Kswapd pages reclaimed            2073183     2108388
Direct pages reclaimed             124909      120577
Percentage direct scans                5%          5%
THP fault alloc                       599         652
THP collapse alloc                    323         354
THP splits                              0           0
THP fault fallback                    806         793
THP collapse fail                      17          16
Compaction stalls                    2457        2025
Compaction success                    906         518
Compaction failures                  1551        1507
Page migrate success              2031423     2360608
Page migrate failure                32845       40852
Compaction pages isolated         4129761     4802025
Compaction migrate scanned       11996712    21750613
Compaction free scanned         214970969   344372001
Compaction cost                      2271        2694

In this scenario, this patch doesn't change the overall success rate as
direct compaction already tries all it can.  There's however significant
reduction in direct compaction stalls (that is, the number of
allocations that went into direct compaction).  The number of successes
(i.e.  direct compaction stalls that ended up with successful
allocation) is reduced by the same number.  This means the offload to
kcompactd is working as expected, and direct compaction is reduced
either due to detecting contention, or compaction deferred by kcompactd.
In the previous version of this patchset there was some apparent
reduction of success rate, but the changes in this version (such as
using sync compaction only), new baseline kernel, and/or averaging
results from 5 executions (my bet), made this go away.

Ftrace-based stats seem to roughly agree:

Time kswapd awake               2532984     2326824
Time kcompactd awake                  0      257916
Time direct compacting           864839      735130
Time kswapd compacting                0           0
Time kcompactd compacting             0      257585

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-03-17 15:09:34 -07:00
Vlastimil Babka
698b1b3064 mm, compaction: introduce kcompactd 
Memory compaction can be currently performed in several contexts:

 - kswapd balancing a zone after a high-order allocation failure
 - direct compaction to satisfy a high-order allocation, including THP
   page fault attemps
 - khugepaged trying to collapse a hugepage
 - manually from /proc

The purpose of compaction is two-fold.  The obvious purpose is to
satisfy a (pending or future) high-order allocation, and is easy to
evaluate.  The other purpose is to keep overal memory fragmentation low
and help the anti-fragmentation mechanism.  The success wrt the latter
purpose is more

The current situation wrt the purposes has a few drawbacks:

 - compaction is invoked only when a high-order page or hugepage is not
   available (or manually).  This might be too late for the purposes of
   keeping memory fragmentation low.
 - direct compaction increases latency of allocations.  Again, it would
   be better if compaction was performed asynchronously to keep
   fragmentation low, before the allocation itself comes.
 - (a special case of the previous) the cost of compaction during THP
   page faults can easily offset the benefits of THP.
 - kswapd compaction appears to be complex, fragile and not working in
   some scenarios.  It could also end up compacting for a high-order
   allocation request when it should be reclaiming memory for a later
   order-0 request.

To improve the situation, we should be able to benefit from an
equivalent of kswapd, but for compaction - i.e. a background thread
which responds to fragmentation and the need for high-order allocations
(including hugepages) somewhat proactively.

One possibility is to extend the responsibilities of kswapd, which could
however complicate its design too much.  It should be better to let
kswapd handle reclaim, as order-0 allocations are often more critical
than high-order ones.

Another possibility is to extend khugepaged, but this kthread is a
single instance and tied to THP configs.

This patch goes with the option of a new set of per-node kthreads called
kcompactd, and lays the foundations, without introducing any new
tunables.  The lifecycle mimics kswapd kthreads, including the memory
hotplug hooks.

For compaction, kcompactd uses the standard compaction_suitable() and
ompact_finished() criteria and the deferred compaction functionality.
Unlike direct compaction, it uses only sync compaction, as there's no
allocation latency to minimize.

This patch doesn't yet add a call to wakeup_kcompactd.  The kswapd
compact/reclaim loop for high-order pages will be replaced by waking up
kcompactd in the next patch with the description of what's wrong with
the old approach.

Waking up of the kcompactd threads is also tied to kswapd activity and
follows these rules:
 - we don't want to affect any fastpaths, so wake up kcompactd only from
   the slowpath, as it's done for kswapd
 - if kswapd is doing reclaim, it's more important than compaction, so
   don't invoke kcompactd until kswapd goes to sleep
 - the target order used for kswapd is passed to kcompactd

Future possible future uses for kcompactd include the ability to wake up
kcompactd on demand in special situations, such as when hugepages are
not available (currently not done due to __GFP_NO_KSWAPD) or when a
fragmentation event (i.e.  __rmqueue_fallback()) occurs.  It's also
possible to perform periodic compaction with kcompactd.

[arnd@arndb.de: fix build errors with kcompactd]
[paul.gortmaker@windriver.com: don't use modular references for non modular code]
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-03-17 15:09:34 -07:00
Joonsoo Kim
7cf91a98e6 mm/compaction: speed up pageblock_pfn_to_page() when zone is contiguous 
There is a performance drop report due to hugepage allocation and in
there half of cpu time are spent on pageblock_pfn_to_page() in
compaction [1].

In that workload, compaction is triggered to make hugepage but most of
pageblocks are un-available for compaction due to pageblock type and
skip bit so compaction usually fails.  Most costly operations in this
case is to find valid pageblock while scanning whole zone range.  To
check if pageblock is valid to compact, valid pfn within pageblock is
required and we can obtain it by calling pageblock_pfn_to_page().  This
function checks whether pageblock is in a single zone and return valid
pfn if possible.  Problem is that we need to check it every time before
scanning pageblock even if we re-visit it and this turns out to be very
expensive in this workload.

Although we have no way to skip this pageblock check in the system where
hole exists at arbitrary position, we can use cached value for zone
continuity and just do pfn_to_page() in the system where hole doesn't
exist.  This optimization considerably speeds up in above workload.

Before vs After
  Max: 1096 MB/s vs 1325 MB/s
  Min: 635 MB/s 1015 MB/s
  Avg: 899 MB/s 1194 MB/s

Avg is improved by roughly 30% [2].

[1]: http://www.spinics.net/lists/linux-mm/msg97378.html
[2]: https://lkml.org/lkml/2015/12/9/23

[akpm@linux-foundation.org: don't forget to restore zone->contiguous on error path, per Vlastimil]
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Reported-by: Aaron Lu <aaron.lu@intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Aaron Lu <aaron.lu@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-03-15 16:55:16 -07:00
Joonsoo Kim
e1409c325f mm/compaction: pass only pageblock aligned range to pageblock_pfn_to_page 
pageblock_pfn_to_page() is used to check there is valid pfn and all
pages in the pageblock is in a single zone.  If there is a hole in the
pageblock, passing arbitrary position to pageblock_pfn_to_page() could
cause to skip whole pageblock scanning, instead of just skipping the
hole page.  For deterministic behaviour, it's better to always pass
pageblock aligned range to pageblock_pfn_to_page().  It will also help
further optimization on pageblock_pfn_to_page() in the following patch.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Aaron Lu <aaron.lu@intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-03-15 16:55:16 -07:00
Joonsoo Kim
623446e4dc mm/compaction: fix invalid free_pfn and compact_cached_free_pfn 
free_pfn and compact_cached_free_pfn are the pointer that remember
restart position of freepage scanner.  When they are reset or invalid,
we set them to zone_end_pfn because freepage scanner works in reverse
direction.  But, because zone range is defined as [zone_start_pfn,
zone_end_pfn), zone_end_pfn is invalid to access.  Therefore, we should
not store it to free_pfn and compact_cached_free_pfn.  Instead, we need
to store zone_end_pfn - 1 to them.  There is one more thing we should
consider.  Freepage scanner scan reversely by pageblock unit.  If
free_pfn and compact_cached_free_pfn are set to middle of pageblock, it
regards that sitiation as that it already scans front part of pageblock
so we lose opportunity to scan there.  To fix-up, this patch do
round_down() to guarantee that reset position will be pageblock aligned.

Note that thanks to the current pageblock_pfn_to_page() implementation,
actual access to zone_end_pfn doesn't happen until now.  But, following
patch will change pageblock_pfn_to_page() so this patch is needed from
now on.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Aaron Lu <aaron.lu@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-03-15 16:55:16 -07:00
Joonsoo Kim
7546934570 mm/compaction.c: __compact_pgdat() code cleanuup 
This patch uses is_via_compact_memory() to distinguish compaction from
sysfs or sysctl.  And, this patch also reduces indentation on
compaction_defer_reset() by filtering these cases first before checking
watermark.

There is no functional change.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-01-14 16:00:49 -08:00
Yaowei Bai
fec4eb2c8d mm/compaction: improve comment for compact_memory tunable knob handler 
sysctl_compaction_handler() is the handler function for compact_memory
tunable knob under /proc/sys/vm, add the missing knob name to make this
more accurate in comment.

No functional change.

Signed-off-by: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2016-01-14 16:00:49 -08:00
Vlastimil Babka
2d1e10412c mm, compaction: distinguish contended status in tracepoints 
Compaction returns prematurely with COMPACT_PARTIAL when contended or has
fatal signal pending.  This is ok for the callers, but might be misleading
in the traces, as the usual reason to return COMPACT_PARTIAL is that we
think the allocation should succeed.  After this patch we distinguish the
premature ending condition in the mm_compaction_finished and
mm_compaction_end tracepoints.

The contended status covers the following reasons:
- lock contention or need_resched() detected in async compaction
- fatal signal pending
- too many pages isolated in the zone (only for async compaction)
Further distinguishing the exact reason seems unnecessary for now.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 2015-11-05 19:34:48 -08:00