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ksm: unmerge is an origin of OOMs

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Just as the swapoff system call allocates many pages of RAM to various
processes, perhaps triggering OOM, so "echo 2 >/sys/kernel/mm/ksm/run"
(unmerge) is liable to allocate many pages of RAM to various processes,
perhaps triggering OOM; and each is normally run from a modest admin
process (swapoff or shell), easily repeated until it succeeds.

So treat unmerge_and_remove_all_rmap_items() in the same way that we treat
try_to_unuse(): generalize PF_SWAPOFF to PF_OOM_ORIGIN, and bracket both
with that, to ask the OOM killer to kill them first, to prevent them from
spawning more and more OOM kills.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2009-09-21 17:02:27 -07:00 committed by Linus Torvalds
parent a913e182ab
commit 35451beecb
4 changed files with 6 additions and 4 deletions
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2
include/linux/sched.h
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@ -1720,7 +1720,7 @@ extern cputime_t task_gtime(struct task_struct *p);
#define PF_FROZEN 0x00010000 /* frozen for system suspend */
#define PF_FSTRANS 0x00020000 /* inside a filesystem transaction */
#define PF_KSWAPD 0x00040000 /* I am kswapd */
#define PF_SWAPOFF 0x00080000 /* I am in swapoff */
#define PF_OOM_ORIGIN 0x00080000 /* Allocating much memory to others */
#define PF_LESS_THROTTLE 0x00100000 /* Throttle me less: I clean memory */
#define PF_KTHREAD 0x00200000 /* I am a kernel thread */
#define PF_RANDOMIZE 0x00400000 /* randomize virtual address space */

2
mm/ksm.c
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@ -1557,7 +1557,9 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
if (ksm_run != flags) {
ksm_run = flags;
if (flags & KSM_RUN_UNMERGE) {
current->flags |= PF_OOM_ORIGIN;
err = unmerge_and_remove_all_rmap_items();
current->flags &= ~PF_OOM_ORIGIN;
if (err) {
ksm_run = KSM_RUN_STOP;
count = err;

2
mm/oom_kill.c
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@ -79,7 +79,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
/*
* swapoff can easily use up all memory, so kill those first.
*/
if (p->flags & PF_SWAPOFF)
if (p->flags & PF_OOM_ORIGIN)
return ULONG_MAX;
/*

4
mm/swapfile.c
View File

@ -1575,9 +1575,9 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
p->flags &= ~SWP_WRITEOK;
spin_unlock(&swap_lock);
current->flags |= PF_SWAPOFF;
current->flags |= PF_OOM_ORIGIN;
err = try_to_unuse(type);
current->flags &= ~PF_SWAPOFF;
current->flags &= ~PF_OOM_ORIGIN;
if (err) {
/* re-insert swap space back into swap_list */