From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753242Ab1GVJTl (ORCPT ); Fri, 22 Jul 2011 05:19:41 -0400 Received: from cantor2.suse.de ([195.135.220.15]:54863 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752260Ab1GVJTk (ORCPT ); Fri, 22 Jul 2011 05:19:40 -0400 Date: Fri, 22 Jul 2011 11:19:36 +0200 From: Michal Hocko To: KAMEZAWA Hiroyuki Cc: linux-mm@kvack.org, Balbir Singh , Daisuke Nishimura , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/4] memcg: do not try to drain per-cpu caches without pages Message-ID: <20110722091936.GB4004@tiehlicka.suse.cz> References: <113c4affc2f0938b7b22d43c88d2b0a623de9a6b.1311241300.git.mhocko@suse.cz> <20110721191250.1c945740.kamezawa.hiroyu@jp.fujitsu.com> <20110721113606.GA27855@tiehlicka.suse.cz> <20110722084413.9dd4b880.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110722084413.9dd4b880.kamezawa.hiroyu@jp.fujitsu.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 22-07-11 08:44:13, KAMEZAWA Hiroyuki wrote: > On Thu, 21 Jul 2011 13:36:06 +0200 > Michal Hocko wrote: > > > On Thu 21-07-11 19:12:50, KAMEZAWA Hiroyuki wrote: > > > On Thu, 21 Jul 2011 09:38:00 +0200 > > > Michal Hocko wrote: > > > > > > > drain_all_stock_async tries to optimize a work to be done on the work > > > > queue by excluding any work for the current CPU because it assumes that > > > > the context we are called from already tried to charge from that cache > > > > and it's failed so it must be empty already. > > > > While the assumption is correct we can do it by checking the current > > > > number of pages in the cache. This will also reduce a work on other CPUs > > > > with an empty stock. > > > > > > > > Signed-off-by: Michal Hocko > > > > > > > > > At the first look, when a charge against TransParentHugepage() goes > > > into the reclaim routine, stock->nr_pages != 0 and this will > > > call additional kworker. > > > > True. We will drain a charge which could be used by other allocations > > in the meantime so we have a good chance to reclaim less. But how big > > problem is that? > > I mean I can add a new parameter that would force checking the current > > cpu but it doesn't look nice. I cannot add that condition > > unconditionally because the code will be shared with the sync path in > > the next patch and that one needs to drain _all_ cpus. > > > > What would you suggest? > By 2 methods > > - just check nr_pages. Not sure I understand which nr_pages you mean. The one that comes from the charging path or stock->nr_pages? If you mean the first one then we do not have in the reclaim path where we call drain_all_stock_async. > - drain "local stock" without calling schedule_work(). It's fast. but there is nothing to be drained locally in the paths where we call drain_all_stock_async... Or do you mean that drain_all_stock shouldn't use work queue at all? > > Thanks, > -Kame -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic