lkml.org 
[lkml]   [2014]   [Oct]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 4/4] mm: numa: Do not mark PTEs pte_numa when splitting huge pages
On Thu, Oct 02, 2014 at 02:29:18PM +0100, Mel Gorman wrote:
> This patch reverts 1ba6e0b50b ("mm: numa: split_huge_page: transfer the
> NUMA type from the pmd to the pte"). If a huge page is being split due
> a protection change and the tail will be in a PROT_NONE vma then NUMA
> hinting PTEs are temporarily created in the protected VMA.
>
> VM_RW|VM_PROTNONE
> |-----------------|
> ^
> split here
>
> In the specific case above, it should get fixed up by change_pte_range()
> but there is a window of opportunity for weirdness to happen. Similarly,
> if a huge page is shrunk and split during a protection update but before
> pmd_numa is cleared then a pte_numa can be left behind.
>
> Instead of adding complexity trying to deal with the case, this patch
> will not mark PTEs NUMA when splitting a huge page. NUMA hinting faults
> will not be triggered which is marginal in comparison to the complexity
> in dealing with the corner cases during THP split.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>

I think it deserves a comment to avoid re-introducing NUMA type
transferring.

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

--
Kirill A. Shutemov


\
 
 \ /
  Last update: 2014-10-02 18:01    [W:0.656 / U:0.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site