linux-kernel - Re: [PATCH v5] memcg: remove PCG_CACHE page

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Message-ID: <20120125133645.GC7694@cmpxchg.org>
Date:	Wed, 25 Jan 2012 14:36:45 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Michal Hocko <mhocko@...e.cz>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hughd@...gle.com>, Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH v5] memcg: remove PCG_CACHE page_cgroup flag

On Wed, Jan 25, 2012 at 02:41:00PM +0900, KAMEZAWA Hiroyuki wrote:
> Subject: [PATCH v5] memcg: remove PCG_CACHE
> 
> We record 'the page is cache' by PCG_CACHE bit to page_cgroup.
> Here, "CACHE" means anonymous user pages (and SwapCache). This
> doesn't include shmem.
> 
> Consdering callers, at charge/uncharge, the caller should know
> what  the page is and we don't need to record it by using 1bit
> per page.
> 
> This patch removes PCG_CACHE bit and make callers of
> mem_cgroup_charge_statistics() to specify what the page is.
> 
> About page migration:
> Mapping of the used page is not touched during migration (see
> page_remove_rmap) so we can rely on it and push the correct charge type
> down to __mem_cgroup_uncharge_common from end_migration for unused page.
> The force flag was misleading was abused for skipping the needless
> page_mapped() / PageCgroupMigration() check, as we know the unused page
> is no longer mapped and cleared the migration flag just a few lines
> up.  But doing the checks is no biggie and it's not worth adding another
> flag just to skip them.
> 
> Changelog since v4
>  - fixed a bug at page migration by Michal Hokko.
> 
> Changelog since v3
>  - renamed a variable 'rss' to 'anon'
> 
> Changelog since v2
>  - removed 'not_rss', added 'anon'
>  - changed a meaning of arguments to mem_cgroup_charge_statisitcs()
>  - removed a patch to mem_cgroup_uncharge_cache
>  - simplified comment.
> 
> Changelog since RFC.
>  - rebased onto memcg-devel
>  - rename 'file' to 'not_rss'
>  - some cleanup and added comment.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>
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