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

[Andrew Morton <akpm@linux-foundation.org>]

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?

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