* [PATCH] mm/mempolicy.c: fix pgoff in mbind vma merge @ 2011-08-01 15:28 Caspar Zhang 2011-08-26 21:23 ` Andrew Morton 0 siblings, 1 reply; 3+ messages in thread From: Caspar Zhang @ 2011-08-01 15:28 UTC (permalink / raw) To: Andrew Morton; +Cc: Caspar Zhang, linux-mm, KOSAKI Motohiro, LKML commit 9d8cebd4bcd7c3878462fdfda34bbcdeb4df7ef4 didn't real fix the mbind vma merge problem due to wrong pgoff value passing to vma_merge(), which made vma_merge() always return NULL. Re-tested the patched kernel with the reproducer provided in commit 9d8cebd, got correct result like below: addr = 0x7ffa5aaa2000 [snip] 7ffa5aaa2000-7ffa5aaa6000 rw-p 00000000 00:00 0 7fffd556f000-7fffd5584000 rw-p 00000000 00:00 0 [stack] Signed-off-by: Caspar Zhang <caspar@casparzhang.com> --- mm/mempolicy.c | 5 ++--- 1 files changed, 2 insertions(+), 3 deletions(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 8b57173..b1f70d6 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -636,7 +636,6 @@ static int mbind_range(struct mm_struct *mm, unsigned long start, struct vm_area_struct *prev; struct vm_area_struct *vma; int err = 0; - pgoff_t pgoff; unsigned long vmstart; unsigned long vmend; @@ -649,9 +648,9 @@ static int mbind_range(struct mm_struct *mm, unsigned long start, vmstart = max(start, vma->vm_start); vmend = min(end, vma->vm_end); - pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags, - vma->anon_vma, vma->vm_file, pgoff, new_pol); + vma->anon_vma, vma->vm_file, vma->vm_pgoff, + new_pol); if (prev) { vma = prev; next = vma->vm_next; -- 1.7.6 ^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/mempolicy.c: fix pgoff in mbind vma merge 2011-08-01 15:28 [PATCH] mm/mempolicy.c: fix pgoff in mbind vma merge Caspar Zhang @ 2011-08-26 21:23 ` Andrew Morton 2011-08-27 2:50 ` Caspar Zhang 0 siblings, 1 reply; 3+ messages in thread From: Andrew Morton @ 2011-08-26 21:23 UTC (permalink / raw) To: Caspar Zhang; +Cc: linux-mm, KOSAKI Motohiro, LKML On Mon, 1 Aug 2011 23:28:55 +0800 Caspar Zhang <caspar@casparzhang.com> wrote: > commit 9d8cebd4bcd7c3878462fdfda34bbcdeb4df7ef4 didn't real fix the > mbind vma merge problem due to wrong pgoff value passing to vma_merge(), > which made vma_merge() always return NULL. > > Re-tested the patched kernel with the reproducer provided in commit > 9d8cebd, got correct result like below: > > addr = 0x7ffa5aaa2000 > [snip] > 7ffa5aaa2000-7ffa5aaa6000 rw-p 00000000 00:00 0 > 7fffd556f000-7fffd5584000 rw-p 00000000 00:00 0 [stack] > Please also describe the output before the patch is applied, and tell us what you believe is wrong with it? > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -636,7 +636,6 @@ static int mbind_range(struct mm_struct *mm, unsigned long start, > struct vm_area_struct *prev; > struct vm_area_struct *vma; > int err = 0; > - pgoff_t pgoff; > unsigned long vmstart; > unsigned long vmend; > > @@ -649,9 +648,9 @@ static int mbind_range(struct mm_struct *mm, unsigned long start, > vmstart = max(start, vma->vm_start); > vmend = min(end, vma->vm_end); > > - pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); > prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags, > - vma->anon_vma, vma->vm_file, pgoff, new_pol); > + vma->anon_vma, vma->vm_file, vma->vm_pgoff, > + new_pol); > if (prev) { > vma = prev; > next = vma->vm_next; > -- > 1.7.6 ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/mempolicy.c: fix pgoff in mbind vma merge 2011-08-26 21:23 ` Andrew Morton @ 2011-08-27 2:50 ` Caspar Zhang 0 siblings, 0 replies; 3+ messages in thread From: Caspar Zhang @ 2011-08-27 2:50 UTC (permalink / raw) To: Andrew Morton; +Cc: linux-mm, KOSAKI Motohiro, LKML On 08/27/2011 05:23 AM, Andrew Morton wrote: > On Mon, 1 Aug 2011 23:28:55 +0800 > Caspar Zhang<caspar@casparzhang.com> wrote: > >> commit 9d8cebd4bcd7c3878462fdfda34bbcdeb4df7ef4 didn't real fix the >> mbind vma merge problem due to wrong pgoff value passing to vma_merge(), >> which made vma_merge() always return NULL. >> >> Re-tested the patched kernel with the reproducer provided in commit >> 9d8cebd, got correct result like below: >> >> addr = 0x7ffa5aaa2000 >> [snip] >> 7ffa5aaa2000-7ffa5aaa6000 rw-p 00000000 00:00 0 >> 7fffd556f000-7fffd5584000 rw-p 00000000 00:00 0 [stack] >> > > Please also describe the output before the patch is applied, and tell > us what you believe is wrong with it? Sure. Before the patch applied, we are getting a result like: addr = 0x7fa58f00c000 [snip] 7fa58f00c000-7fa58f00d000 rw-p 00000000 00:00 0 7fa58f00d000-7fa58f00e000 rw-p 00000000 00:00 0 7fa58f00e000-7fa58f00f000 rw-p 00000000 00:00 0 here 7fa58f00c000->7fa58f00f000 we get 3 VMAs which are expected to be merged described in commit 9d8cebd. commit 9d8cebd says: ------------------------------------------------------------------- commit 9d8cebd4bcd7c3878462fdfda34bbcdeb4df7ef4 Author: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Date: Fri Mar 5 13:41:57 2010 -0800 mm: fix mbind vma merge problem Strangely, current mbind() doesn't merge vma with neighbor vma although it's possible. Unfortunately, many vma can reduce performance... This patch fixes it. ------------------------------------------------------------------- mbind_range() invokes vma_range() to merge current VMA with its successor: prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags, vma->anon_vma, vma->vm_file, pgoff, new_pol); in vma_merge(), it should go into: if (next && end == next->vm_start && mpol_equal(policy, vma_policy(next)) && can_vma_merge_before(next, vm_flags, anon_vma, file, pgoff+pglen)) { ... } while in can_vma_merge_before(), we have: static int can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags, struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff) { if (is_mergeable_vma(vma, file, vm_flags) && is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) { if (vma->vm_pgoff == vm_pgoff) return 1; } return 0; } to make can_vma_merge_before() return 1, we should have (next->vm_pgoff == pgoff + pglen) in vma_merge(), i.e., pgoff should be the page offset of *current* VMA. However from the current codes in mbind_range(), we get: pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); start is the beginning addr of the range, so here pgoff will always be the page offset of the beginning VMA, that makes merging VMAs impossible in mbind_range(). To solve this bug, we simply need to pass vma->pgoff instead of the calculated pgoff value to vma_merge(). Thanks, Caspar > >> --- a/mm/mempolicy.c >> +++ b/mm/mempolicy.c >> @@ -636,7 +636,6 @@ static int mbind_range(struct mm_struct *mm, unsigned long start, >> struct vm_area_struct *prev; >> struct vm_area_struct *vma; >> int err = 0; >> - pgoff_t pgoff; >> unsigned long vmstart; >> unsigned long vmend; >> >> @@ -649,9 +648,9 @@ static int mbind_range(struct mm_struct *mm, unsigned long start, >> vmstart = max(start, vma->vm_start); >> vmend = min(end, vma->vm_end); >> >> - pgoff = vma->vm_pgoff + ((start - vma->vm_start)>> PAGE_SHIFT); >> prev = vma_merge(mm, prev, vmstart, vmend, vma->vm_flags, >> - vma->anon_vma, vma->vm_file, pgoff, new_pol); >> + vma->anon_vma, vma->vm_file, vma->vm_pgoff, >> + new_pol); >> if (prev) { >> vma = prev; >> next = vma->vm_next; >> -- >> 1.7.6 ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2011-08-27 2:52 UTC | newest] Thread overview: 3+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2011-08-01 15:28 [PATCH] mm/mempolicy.c: fix pgoff in mbind vma merge Caspar Zhang 2011-08-26 21:23 ` Andrew Morton 2011-08-27 2:50 ` Caspar Zhang
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