lkml.org 
[lkml]   [2012]   [Sep]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] hugetlb: do not use vma_hugecache_offset for vma_prio_tree_foreach
On Mon, Aug 13, 2012 at 03:55:41PM +0200, Michal Hocko wrote:
> 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 so the standard PAGE_SHIFT based
> index calculation is used instead.

I do think it's incorrect. The resulting index may not be too big,
but it can be too small: assume hpage size of 2M and the address to
unmap to be 0x200000. This is regular page index 512 and hpage index
1. If you have a VMA that maps the file only starting at the second
huge page, that VMAs vm_pgoff will be 512 but you ask for offset 1 and
miss it even though it does map the page of interest. hugetlb_cow()
will try to unmap, miss the vma, and retry the cow until the
allocation succeeds or the skipped vma(s) go away.

Unless I missed something, this should not be deferred as a cleanup.


\
 
 \ /
  Last update: 2012-09-26 23:41    [W:0.069 / U:0.432 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site