Re: [RFC][PATCH 1/6] memcg: free all at rmdir

KAMEZAWA Hiroyuki
2008-11-13T01:15:37Z

On Wed, 12 Nov 2008 16:07:58 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Wed, 12 Nov 2008 12:26:56 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>
> > +5.1 on_rmdir
> > +set behavior of memcg at rmdir (Removing cgroup) default is "drop".
> > +
> > +5.1.1 drop
> > + #echo on_rmdir drop > memory.attribute
> > + This is default. All pages on the memcg will be freed.
> > + If pages are locked or too busy, they will be moved up to the parent.
> > + Useful when you want to drop (large) page caches used in this memcg.
> > + But some of in-use page cache can be dropped by this.
> > +
> > +5.1.2 keep
> > + #echo on_rmdir keep > memory.attribute
> > + All pages on the memcg will be moved to its parent.
> > + Useful when you don't want to drop page caches used in this memcg.
> > + You can keep page caches from some library or DB accessed by this
> > + memcg on memory.
>
> Would it not be more useful to implement a per-memcg version of
> /proc/sys/vm/drop_caches? (One without drop_caches' locking bug,
> hopefully).
>
> If we do this then we can make the above "keep" behaviour non-optional,
> and the operator gets to choose whether or not to drop the caches
> before doing the rmdir.
>
> Plus, we get a new per-memcg drop_caches capability. And it's a nicer
> interface, and it doesn't have the obvious races which on_rmdir has,
> etc.
>
> hm?
>
In my plan, I'll add

memory.shrink_usage interface to do and allows

#echo 0M > memory.shrink_memory_usage
(you may swap tasks out if there is task..)

to drop pages.

Balbir, how do you think ? I've already removed "force_empty".

Thanks,
-Kame