linux-kernel - Re: [patch] hugetlb: correct page offset index for sharing pmd

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Date:	Fri, 10 Aug 2012 15:16:43 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [patch] hugetlb: correct page offset index for sharing pmd

[CCing Kamezawa and David]

On Fri 10-08-12 20:53:36, Hillf Danton wrote:
> On Fri, Aug 10, 2012 at 8:51 PM, Michal Hocko <mhocko@...e.cz> wrote:
> > On Fri 10-08-12 20:37:20, Hillf Danton wrote:
> >> On Fri, Aug 10, 2012 at 8:27 PM, Michal Hocko <mhocko@...e.cz> wrote:
> >> >
> >> > I guess you mean unmap_ref_private and that has been changed by you
> >> > (0c176d5 mm: hugetlb: fix pgoff computation when unmapping page from
> >> > vma)...  I was wrong at that time when giving my Reviewed-by. The patch
> >> > didn't break anything because you still find all relevant vmas because
> >> > vma_hugecache_offset just provides a smaller index which is still within
> >> > boundaries.
> >>
> >> No, as shown by the log message of 0c176d52b,  that fix was
> >> triggered by  (vma->vm_pgoff >> PAGE_SHIFT), thus I dont see
> >> what you really want to revert.
> >
> > fix for that would be a part of the revert of course.
> >
> 
> Fine, go ahead ;)

there you go
---
>From 973187e9bad72181f4563a675ca64235f8612a2a Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.cz>
Date: Fri, 10 Aug 2012 15:03:07 +0200
Subject: [PATCH] hugetlb: do not use vma_hugecache_offset for
 vma_prio_tree_foreach

0c176d5 (mm: hugetlb: fix pgoff computation when unmapping page
from vma) fixed pgoff calculation but it has replaced it by
vma_hugecache_offset which is not approapriate for offsets used for
vma_prio_tree_foreach because that one expects index in page units
rather than in huge_page_shift.
Using vma_hugecache_offset is not incorrect because the pgoff will fit
into the same vmas but it is confusing.

Cc: Hillf Danton <dhillf@...il.com>
Cc: Mel Gorman <mel@....ul.ie>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: David Rientjes <rientjes@...gle.com>
Signed-off-by: Michal Hocko <mhocko@...e.cz>
---
 mm/hugetlb.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c39e4be..a74ea31 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2462,7 +2462,8 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
 	 * from page cache lookup which is in HPAGE_SIZE units.
 	 */
 	address = address & huge_page_mask(h);
-	pgoff = vma_hugecache_offset(h, vma, address);
+	pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) +
+			vma->vm_pgoff;
 	mapping = vma->vm_file->f_dentry->d_inode->i_mapping;
 
 	/*
-- 
1.7.10.4


-- 
Michal Hocko
SUSE Labs
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