From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx170.postini.com [74.125.245.170]) by kanga.kvack.org (Postfix) with SMTP id 2EBAA6B0068 for ; Mon, 1 Oct 2012 04:48:38 -0400 (EDT) Message-ID: <50695817.2030201@parallels.com> Date: Mon, 1 Oct 2012 12:45:11 +0400 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH v3 04/13] kmem accounting basic infrastructure References: <50635B9D.8020205@parallels.com> <20120926195648.GA20342@google.com> <50635F46.7000700@parallels.com> <20120926201629.GB20342@google.com> <50637298.2090904@parallels.com> <20120927120806.GA29104@dhcp22.suse.cz> <20120927143300.GA4251@mtj.dyndns.org> <20120927144307.GH3429@suse.de> <20120927145802.GC4251@mtj.dyndns.org> <50649B4C.8000208@parallels.com> <20120930082358.GG10383@mtj.dyndns.org> In-Reply-To: <20120930082358.GG10383@mtj.dyndns.org> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: Mel Gorman , Michal Hocko , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, kamezawa.hiroyu@jp.fujitsu.com, devel@openvz.org, linux-mm@kvack.org, Suleiman Souhlal , Frederic Weisbecker , David Rientjes , Johannes Weiner On 09/30/2012 12:23 PM, Tejun Heo wrote: > Hello, Glauber. > > On Thu, Sep 27, 2012 at 10:30:36PM +0400, Glauber Costa wrote: >>> But that happens only when pages enter and leave slab and if it still >>> is significant, we can try to further optimize charging. Given that >>> this is only for cases where memcg is already in use and we provide a >>> switch to disable it globally, I really don't think this warrants >>> implementing fully hierarchy configuration. >> >> Not totally true. We still have to match every allocation to the right >> cache, and that is actually our heaviest hit, responsible for the 2, 3 % >> we're seeing when this is enabled. It is the kind of path so hot that >> people frown upon branches being added, so I don't think we'll ever get >> this close to being free. > > Sure, depening on workload, any addition to alloc/free could be > noticeable. I don't know. I'll write more about it when replying to > Michal's message. BTW, __memcg_kmem_get_cache() does seem a bit > heavy. I wonder whether indexing from cache side would make it > cheaper? e.g. something like the following. > > kmem_cache *__memcg_kmem_get_cache(cachep, gfp) > { > struct kmem_cache *c; > > c = cachep->memcg_params->caches[percpu_read(kmemcg_slab_idx)]; > if (likely(c)) > return c; > /* try to create and then fall back to cachep */ > } > > where kmemcg_slab_idx is updated from sched notifier (or maybe add and > use current->kmemcg_slab_idx?). You would still need __GFP_* and > in_interrupt() tests but current->mm and PF_KTHREAD tests can be > rolled into index selection. > How big would this array be? there can be a lot more kmem_caches than there are memcgs. That is why it is done from memcg side. -- 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