From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx160.postini.com [74.125.245.160]) by kanga.kvack.org (Postfix) with SMTP id 72BED6B0031 for ; Wed, 5 Jun 2013 04:45:00 -0400 (EDT) Received: by mail-pd0-f178.google.com with SMTP id w16so1500578pde.9 for ; Wed, 05 Jun 2013 01:44:59 -0700 (PDT) Date: Wed, 5 Jun 2013 01:44:56 -0700 From: Tejun Heo Subject: Re: [PATCH 3/3] memcg: simplify mem_cgroup_reclaim_iter Message-ID: <20130605084456.GA7990@mtj.dyndns.org> References: <1370306679-13129-1-git-send-email-tj@kernel.org> <1370306679-13129-4-git-send-email-tj@kernel.org> <20130604131843.GF31242@dhcp22.suse.cz> <20130604205025.GG14916@htj.dyndns.org> <20130604212808.GB13231@dhcp22.suse.cz> <20130604215535.GM14916@htj.dyndns.org> <20130605073023.GB15997@dhcp22.suse.cz> <20130605082023.GG7303@mtj.dyndns.org> <20130605083628.GE15997@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130605083628.GE15997@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: hannes@cmpxchg.org, bsingharora@gmail.com, cgroups@vger.kernel.org, linux-mm@kvack.org, lizefan@huawei.com Hey, On Wed, Jun 05, 2013 at 10:36:28AM +0200, Michal Hocko wrote: > > It's still bound, no? Each live memcg can only keep limited number of > > cgroups cached, right? > > Assuming that they are cleaned up when the memcg is offlined then yes. Oh yeah, that's just me being forgetful. We definitely need to clean it up on offlining. > > Do you think that the number can actually grow harmful? Would you be > > kind enough to share some calculations with me? > > Well, each intermediate node might pin up-to NR_NODES * NR_ZONES * > NR_PRIORITY groups. You would need a big hierarchy to have chance to > cache different groups so that it starts matter. Yeah, NR_NODES can be pretty big. I'm still not sure whether this would be a problem in practice but yeah it can grow pretty big. > And do what? css_try_get to find out whether the cached memcg is still Hmmm? It can just look at the timestamp and if too old do cached = xchg(&iter->hint, NULL); if (cached) css_put(cached); > alive. Sorry, I do not like it at all. I find it much better to clean up > when the group is removed. Because doing things asynchronously just > makes it more obscure. There is no reason to do such a thing on the > background when we know _when_ to do the cleanup and that is definitely > _not a hot path_. Yeah, that's true. I just wanna avoid the barrier dancing. Only one of the ancestors can cache a memcg, right? Walking up the tree scanning for cached ones and putting them should work? Is that what you were suggesting? Thanks. -- tejun -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org