linux-kernel - Re: [PATCH 5/7] memcg: get rid of once-per-second cache shrinking for dead memcgs

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Message-ID: <20121116145508.GC2006@dhcp22.suse.cz>
Date:	Fri, 16 Nov 2012 15:55:08 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Glauber Costa <glommer@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: [PATCH 5/7] memcg: get rid of once-per-second cache shrinking
 for dead memcgs

On Fri 16-11-12 16:21:59, KAMEZAWA Hiroyuki wrote:
> (2012/11/16 16:11), Glauber Costa wrote:
> > On 11/16/2012 09:07 AM, Kamezawa Hiroyuki wrote:
> >> (2012/11/15 22:47), Glauber Costa wrote:
> >>> On 11/15/2012 01:41 PM, Kamezawa Hiroyuki wrote:
> >>>> (2012/11/15 11:54), Glauber Costa wrote:
> >>>>> The idea is to synchronously do it, leaving it up to the shrinking
> >>>>> facilities in vmscan.c and/or others. Not actively retrying shrinking
> >>>>> may leave the caches alive for more time, but it will remove the ugly
> >>>>> wakeups. One would argue that if the caches have free objects but are
> >>>>> not being shrunk, it is because we don't need that memory yet.
> >>>>>
> >>>>> Signed-off-by: Glauber Costa <glommer@...allels.com>
> >>>>> CC: Michal Hocko <mhocko@...e.cz>
> >>>>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> >>>>> CC: Johannes Weiner <hannes@...xchg.org>
> >>>>> CC: Andrew Morton <akpm@...ux-foundation.org>
> >>>>
> >>>> I agree this patch but can we have a way to see the number of unaccounted
> >>>> zombie cache usage for debugging ?
> >>>>
> >>>> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> >>>>
> >>> Any particular interface in mind ?
> >>>
> >>
> >> Hmm, it's debug interface and having cgroup file may be bad.....
> >> If it can be seen in bytes or some, /proc/vmstat ?
> >>
> >> out_of_track_slabs  xxxxxxx. hm ?
> >>
> > 
> > I particularly think that, being this a debug interface, it is also
> > useful to have an indication of which caches are still in place. This is
> > because the cache itself, is the best indication we have about the
> > specific workload that may be keeping it in memory.
> > 
> > I first thought debugfs could help us probing useful information out of
> > it, but given all the abuse people inflicted in debugfs... maybe we
> > could have a file in the root memcg with that information for all
> > removed memcgs? If we do that, we can go further and list the memcgs
> > that are pending due to memsw as well. memory.dangling_memcgs ?
> > 
> 
> Hm, I'm ok with it... others ?

What about memory.kmem.dangling_caches?
-- 
Michal Hocko
SUSE Labs
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