lkml.org 
[lkml]   [2015]   [May]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCHv5 04/28] mm, thp: adjust conditions when we can reuse the page on WP fault
On Fri, May 15, 2015 at 11:15:00AM +0200, Vlastimil Babka wrote:
> On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> >With new refcounting we will be able map the same compound page with
> >PTEs and PMDs. It requires adjustment to conditions when we can reuse
> >the page on write-protection fault.
> >
> >For PTE fault we can't reuse the page if it's part of huge page.
> >
> >For PMD we can only reuse the page if nobody else maps the huge page or
> >it's part. We can do it by checking page_mapcount() on each sub-page,
> >but it's expensive.
> >
> >The cheaper way is to check page_count() to be equal 1: every mapcount
> >takes page reference, so this way we can guarantee, that the PMD is the
> >only mapping.
> >
> >This approach can give false negative if somebody pinned the page, but
> >that doesn't affect correctness.
> >
> >Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> >Tested-by: Sasha Levin <sasha.levin@oracle.com>
>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
>
> So couldn't the same trick be used in Patch 1 to avoid counting individual
> oder-0 pages?

Hm. You're right, we could. But is smaps that performance sensitive to
bother?

--
Kirill A. Shutemov


\
 
 \ /
  Last update: 2015-05-15 18:21    [W:0.177 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site