lkml.org 
[lkml]   [2019]   [Mar]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH REBASED] mm, memcg: Make scan aggression always exclude protection
Date
On Fri, Mar 22, 2019 at 10:49:46PM +0000, Chris Down wrote:
> Roman Gushchin writes:
> > I've noticed that the old version is just wrong: if cgroup_size is way smaller
> > than max(min, low), scan will be set to -lruvec_size.
> > Given that it's unsigned long, we'll end up with scanning the whole list
> > (due to clamp() below).
>
> Are you certain? If so, I don't see what you mean. This is how the code
> looks in Linus' tree after the fixups:
>
> unsigned long cgroup_size = mem_cgroup_size(memcg);
> unsigned long baseline = 0;
>
> if (!sc->memcg_low_reclaim)
> baseline = lruvec_size;
> scan = lruvec_size * cgroup_size / protection - baseline;

>
> This works correctly as far as I can tell:

I'm blaming the old version, not the new one.

New one is perfectly fine, thanks to these lines:
+ /* Avoid TOCTOU with earlier protection check */
+ cgroup_size = max(cgroup_size, protection);

The old one was racy.

Thanks!

\
 
 \ /
  Last update: 2019-03-23 00:02    [W:0.088 / U:16.972 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site