forked from luck/tmp_suning_uos_patched
mm: Check if PTE is already allocated during page fault
With transparent hugepage support, handle_mm_fault() has to be careful that a normal PMD has been established before handling a PTE fault. To achieve this, it used __pte_alloc() directly instead of pte_alloc_map as pte_alloc_map is unsafe to run against a huge PMD. pte_offset_map() is called once it is known the PMD is safe. pte_alloc_map() is smart enough to check if a PTE is already present before calling __pte_alloc but this check was lost. As a consequence, PTEs may be allocated unnecessarily and the page table lock taken. Thi useless PTE does get cleaned up but it's a performance hit which is visible in page_test from aim9. This patch simply re-adds the check normally done by pte_alloc_map to check if the PTE needs to be allocated before taking the page table lock. The effect is noticable in page_test from aim9. AIM9 2.6.38-vanilla 2.6.38-checkptenone creat-clo 446.10 ( 0.00%) 424.47 (-5.10%) page_test 38.10 ( 0.00%) 42.04 ( 9.37%) brk_test 52.45 ( 0.00%) 51.57 (-1.71%) exec_test 382.00 ( 0.00%) 456.90 (16.39%) fork_test 60.11 ( 0.00%) 67.79 (11.34%) MMTests Statistics: duration Total Elapsed Time (seconds) 611.90 612.22 (While this affects 2.6.38, it is a performance rather than a functional bug and normally outside the rules -stable. While the big performance differences are to a microbench, the difference in fork and exec performance may be significant enough that -stable wants to consider the patch) Reported-by: Raz Ben Yehuda <raziebe@gmail.com> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Rik van Riel <riel@redhat.com> [ Picked this up from the AutoNUMA tree to help it upstream and to allow apples-to-apples performance comparisons. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
parent
8d1acce453
commit
4fd017708c
|
@ -710,7 +710,8 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
|
|||
* run pte_offset_map on the pmd, if an huge pmd could
|
||||
* materialize from under us from a different thread.
|
||||
*/
|
||||
if (unlikely(__pte_alloc(mm, vma, pmd, address)))
|
||||
if (unlikely(pmd_none(*pmd)) &&
|
||||
unlikely(__pte_alloc(mm, vma, pmd, address)))
|
||||
return VM_FAULT_OOM;
|
||||
/* if an huge pmd materialized from under us just retry later */
|
||||
if (unlikely(pmd_trans_huge(*pmd)))
|
||||
|
|
|
@ -3560,7 +3560,8 @@ int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
|
|||
* run pte_offset_map on the pmd, if an huge pmd could
|
||||
* materialize from under us from a different thread.
|
||||
*/
|
||||
if (unlikely(pmd_none(*pmd)) && __pte_alloc(mm, vma, pmd, address))
|
||||
if (unlikely(pmd_none(*pmd)) &&
|
||||
unlikely(__pte_alloc(mm, vma, pmd, address)))
|
||||
return VM_FAULT_OOM;
|
||||
/* if an huge pmd materialized from under us just retry later */
|
||||
if (unlikely(pmd_trans_huge(*pmd)))
|
||||
|
|
Loading…
Reference in New Issue
Block a user