[lkml]   [2013]   [Jan]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 7/11] ksm: make KSM page migration possible
On Sun, 27 Jan 2013, Simon Jeons wrote:
> On Sun, 2013-01-27 at 15:12 -0800, Hugh Dickins wrote:
> > On Sat, 26 Jan 2013, Simon Jeons wrote:
> > >
> > > Could you explain why need check page->mapping twice after get page?
> >
> > Once for the !locked case, which should not return page if mapping changed.
> > Once for the locked case, which should not return page if mapping changed.
> > We could use "else", but that wouldn't be an improvement.
> But for locked case, page->mapping will be check twice.


I'm beginning to wonder: you do realize that page->mapping is volatile,
from the point of view of get_ksm_page()? That is the whole point of
why get_ksm_page() exists.

I can see that the word "volatile" is not obviously used here - it's
tucked away inside the ACCESS_ONCE() - but I thought the descriptions
of races and barriers made that obvious.

If the comments here haven't helped enough, please take a look at
git commit 4035c07a8959 "ksm: take keyhole reference to page".

 \ /
  Last update: 2013-01-28 05:21    [W:0.067 / U:0.756 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site