From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta12.messagelabs.com (mail6.bemta12.messagelabs.com [216.82.250.247]) by kanga.kvack.org (Postfix) with ESMTP id BA39B6B016A for ; Fri, 26 Aug 2011 22:52:11 -0400 (EDT) Received: by vxj3 with SMTP id 3so4147879vxj.14 for ; Fri, 26 Aug 2011 19:52:09 -0700 (PDT) Message-ID: <4E585B72.9070401@casparzhang.com> Date: Sat, 27 Aug 2011 10:50:26 +0800 From: Caspar Zhang MIME-Version: 1.0 Subject: Re: [PATCH] mm/mempolicy.c: fix pgoff in mbind vma merge References: <14efb4b829a69f8c13d65de60a4508c0bbb0a5f5.1312212325.git.caspar@casparzhang.com> <20110826142328.ab4726cb.akpm@linux-foundation.org> In-Reply-To: <20110826142328.ab4726cb.akpm@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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 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 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org