From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f174.google.com (mail-pd0-f174.google.com [209.85.192.174]) by kanga.kvack.org (Postfix) with ESMTP id 838CC6B006C for ; Thu, 15 Jan 2015 08:25:28 -0500 (EST) Received: by mail-pd0-f174.google.com with SMTP id fp1so16281253pdb.5 for ; Thu, 15 Jan 2015 05:25:28 -0800 (PST) Received: from mx2.parallels.com (mx2.parallels.com. [199.115.105.18]) by mx.google.com with ESMTPS id fl9si1773180pab.154.2015.01.15.05.25.26 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 15 Jan 2015 05:25:27 -0800 (PST) Date: Thu, 15 Jan 2015 16:25:16 +0300 From: Vladimir Davydov Subject: Re: [PATCH -mm v2] vmscan: move reclaim_state handling to shrink_slab Message-ID: <20150115132516.GG11264@esperanza> References: <1421311073-28130-1-git-send-email-vdavydov@parallels.com> <20150115125820.GE7000@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20150115125820.GE7000@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Johannes Weiner , Vlastimil Babka , Mel Gorman , Rik van Riel , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, Jan 15, 2015 at 01:58:20PM +0100, Michal Hocko wrote: > On Thu 15-01-15 11:37:53, Vladimir Davydov wrote: > > current->reclaim_state is only used to count the number of slab pages > > reclaimed by shrink_slab(). So instead of initializing it before we are > > > > Note that after this patch try_to_free_mem_cgroup_pages() will count not > > only reclaimed user pages, but also slab pages, which is expected, > > because it can reclaim kmem from kmem-active sub cgroups. > > Except that reclaim_state counts all freed slab objects that have > current->reclaim_state != NULL AFAIR. This includes also kfreed pages > from interrupt context and who knows what else and those pages might be > from a different memcgs, no? Hmm, true, good point. Can an interrupt handler free a lot of memory though? Does RCU free objects from irq or soft irq context? > Besides that I am not sure this makes any difference in the end. No > try_to_free_mem_cgroup_pages caller really cares about the exact > number of reclaimed pages. We care only about whether there was any > progress done - and even that not exactly (e.g. try_charge checks > mem_cgroup_margin before retry/oom so if sufficient kmem pages were > uncharged then we will notice that). Frankly, I thought exactly the same initially, that's why I dropped reclaim_state handling from the initial memcg shrinkers patch set. However, then Hillf noticed that nr_reclaimed is checked right after calling shrink_slab() in the memcg iteration loop in shrink_zone(): memcg = mem_cgroup_iter(root, NULL, &reclaim); do { [...] if (memcg && is_classzone) shrink_slab(sc->gfp_mask, zone_to_nid(zone), memcg, sc->nr_scanned - scanned, lru_pages); /* * Direct reclaim and kswapd have to scan all memory * cgroups to fulfill the overall scan target for the * zone. * * Limit reclaim, on the other hand, only cares about * nr_to_reclaim pages to be reclaimed and it will * retry with decreasing priority if one round over the * whole hierarchy is not sufficient. */ if (!global_reclaim(sc) && sc->nr_reclaimed >= sc->nr_to_reclaim) { mem_cgroup_iter_break(root, memcg); break; } memcg = mem_cgroup_iter(root, memcg, &reclaim); } while (memcg); If we can ignore reclaimed slab pages here (?), let's drop this patch. Thanks, Vladimir -- 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