From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx192.postini.com [74.125.245.192]) by kanga.kvack.org (Postfix) with SMTP id 7818C6B0345 for ; Mon, 25 Jun 2012 10:06:48 -0400 (EDT) Message-ID: <4FE86FD8.6010000@parallels.com> Date: Mon, 25 Jun 2012 18:04:08 +0400 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH v4 07/25] memcg: Reclaim when more than one page needed. References: <1340015298-14133-1-git-send-email-glommer@parallels.com> <1340015298-14133-8-git-send-email-glommer@parallels.com> <20120620134738.GG5541@tiehlicka.suse.cz> <4FE227F8.3000504@parallels.com> <20120621211923.GC31759@tiehlicka.suse.cz> <4FE86411.5020708@parallels.com> In-Reply-To: <4FE86411.5020708@parallels.com> Content-Type: multipart/mixed; boundary="------------040608080709070303070003" Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, Pekka Enberg , Cristoph Lameter , David Rientjes , cgroups@vger.kernel.org, devel@openvz.org, kamezawa.hiroyu@jp.fujitsu.com, linux-kernel@vger.kernel.org, Frederic Weisbecker , Suleiman Souhlal --------------040608080709070303070003 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit On 06/25/2012 05:13 PM, Glauber Costa wrote: > >>>>> + >>>>> ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags); >>>>> if (mem_cgroup_margin(mem_over_limit) >= nr_pages) >>>>> return CHARGE_RETRY; >>>>> @@ -2234,8 +2235,10 @@ static int mem_cgroup_do_charge(struct >>>>> mem_cgroup *memcg, gfp_t gfp_mask, >>>>> * unlikely to succeed so close to the limit, and we fall back >>>>> * to regular pages anyway in case of failure. >>>>> */ >>>>> - if (nr_pages == 1 && ret) >>>>> + if (nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER) && ret) { >>>>> + cond_resched(); >>>>> return CHARGE_RETRY; >>>>> + } >>>> >>>> What prevents us from looping for unbounded amount of time here? >>>> Maybe you need to consider the number of reclaimed pages here. >>> >>> Why would we even loop here? It will just return CHARGE_RETRY, it is >>> up to the caller to decide whether or not it will retry. >> >> Yes, but the test was original to prevent oom when we managed to reclaim >> something. And something might be enough for a single page but now you >> have high order allocations so we can retry without any success. >> > > So, > > Most of the kmem allocations are likely to be quite small as well. For > the slab, we're dealing with the order of 2-3 pages, and for other > allocations that may happen, like stack, they will be in the order of 2 > pages as well. > > So one thing I could do here, is define a threshold, say, 3, and only > retry for that very low threshold, instead of following COSTLY_ORDER. > I don't expect two or three pages to be much less likely to be freed > than a single page. > > I am fine with ripping of the cond_resched as well. > > Let me know if you would be okay with that. > > For the record, here's the patch I would propose. At this point, I think it would be nice to Suleiman to say if he is still okay with the changes. --------------040608080709070303070003 Content-Type: text/x-patch; name="0001-memcg-Reclaim-when-more-than-one-page-needed.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="0001-memcg-Reclaim-when-more-than-one-page-needed.patch" --------------040608080709070303070003--