linux-kernel - Re: [PATCH 2/4] memcg: unify sync and async per-cpu charge cache draining

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Message-ID: <20110721113626.GB27855@tiehlicka.suse.cz>
Date:	Thu, 21 Jul 2011 13:36:26 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	linux-mm@...ck.org, Balbir Singh <bsingharora@...il.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] memcg: unify sync and async per-cpu charge cache
 draining

On Thu 21-07-11 19:25:25, KAMEZAWA Hiroyuki wrote:
> On Thu, 21 Jul 2011 09:50:00 +0200
> Michal Hocko <mhocko@...e.cz> wrote:
> 
> > Currently we have two ways how to drain per-CPU caches for charges.
> > drain_all_stock_sync will synchronously drain all caches while
> > drain_all_stock_async will asynchronously drain only those that refer to
> > a given memory cgroup or its subtree in hierarchy.
> > Targeted async draining has been introduced by 26fe6168 (memcg: fix
> > percpu cached charge draining frequency) to reduce the cpu workers
> > number.
> > 
> > sync draining is currently triggered only from mem_cgroup_force_empty
> > which is triggered only by userspace (mem_cgroup_force_empty_write) or
> > when a cgroup is removed (mem_cgroup_pre_destroy). Although these are
> > not usually frequent operations it still makes some sense to do targeted
> > draining as well, especially if the box has many CPUs.
> > 
> > This patch unifies both methods to use the single code (drain_all_stock)
> > which relies on the original async implementation and just adds
> > flush_work to wait on all caches that are still under work for the sync
> > mode.
> > We are using FLUSHING_CACHED_CHARGE bit check to prevent from waiting on
> > a work that we haven't triggered.
> > Please note that both sync and async functions are currently protected
> > by percpu_charge_mutex so we cannot race with other drainers.
> > 
> > Signed-off-by: Michal Hocko <mhocko@...e.cz>
> 
> hmm..maybe good.
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Thanks

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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