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Date: Thu, 12 Jan 2012 08:59:37 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: memcg: add mlock statistic in memory.stat
Message-Id: <20120112085937.ae601869.kamezawa.hiroyu@jp.fujitsu.com>
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	<alpine.LSU.2.00.1201111512570.1846@eggly.anvils>
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To: Hugh Dickins <hughd@google.com>
Cc: Ying Han <yinghan@google.com>, Michal Hocko <mhocko@suse.cz>, Balbir Singh <bsingharora@gmail.com>, Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mel@csn.ul.ie>, Pavel Emelyanov <xemul@openvz.org>, linux-mm@kvack.org

On Wed, 11 Jan 2012 15:17:42 -0800 (PST)
Hugh Dickins <hughd@google.com> wrote:

> On Wed, 11 Jan 2012, Ying Han wrote:
> 
> > We have the nr_mlock stat both in meminfo as well as vmstat system wide, this
> > patch adds the mlock field into per-memcg memory stat. The stat itself enhances
> > the metrics exported by memcg, especially is used together with "uneivctable"
> > lru stat.
> > 
> > --- a/include/linux/page_cgroup.h
> > +++ b/include/linux/page_cgroup.h
> > @@ -10,6 +10,7 @@ enum {
> >  	/* flags for mem_cgroup and file and I/O status */
> >  	PCG_MOVE_LOCK, /* For race between move_account v.s. following bits */
> >  	PCG_FILE_MAPPED, /* page is accounted as "mapped" */
> > +	PCG_MLOCK, /* page is accounted as "mlock" */
> >  	/* No lock in page_cgroup */
> >  	PCG_ACCT_LRU, /* page has been accounted for (under lru_lock) */
> >  	__NR_PCG_FLAGS,
> 
> Is this really necessary?  KAMEZAWA-san is engaged in trying to reduce
> the number of PageCgroup flags, and I expect that in due course we shall
> want to merge them in with Page flags, so adding more is unwelcome.
> I'd  have thought that with memcg_ hooks in the right places,
> a separate flag would not be necessary?
> 

Please don't ;)

NR_UNEIVCTABLE_LRU is not enough ?

Following is the patch I posted before to remove PCG_FILE_MAPPED.
Then, I think you can use similar logic and make use of UNEVICTABLE flags.

==
better (lockless) idea is welcomed.