Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755923AbaJVQLn (ORCPT ); Wed, 22 Oct 2014 12:11:43 -0400 Received: from cantor2.suse.de ([195.135.220.15]:43568 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755899AbaJVQLl (ORCPT ); Wed, 22 Oct 2014 12:11:41 -0400 Date: Wed, 22 Oct 2014 18:11:40 +0200 From: Michal Hocko To: Johannes Weiner Cc: Andrew Morton , Hugh Dickins , Vladimir Davydov , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 4/4] mm: memcontrol: remove unnecessary PCG_USED pc->mem_cgroup valid flag Message-ID: <20141022161140.GG30802@dhcp22.suse.cz> References: <1413818532-11042-1-git-send-email-hannes@cmpxchg.org> <1413818532-11042-5-git-send-email-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1413818532-11042-5-git-send-email-hannes@cmpxchg.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 20-10-14 11:22:12, Johannes Weiner wrote: > pc->mem_cgroup had to be left intact after uncharge for the final LRU > removal, and !PCG_USED indicated whether the page was uncharged. But > since 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API") pages are > uncharged after the final LRU removal. Uncharge can simply clear the > pointer and the PCG_USED/PageCgroupUsed sites can test that instead. > > Because this is the last page_cgroup flag, this patch reduces the > memcg per-page overhead to a single pointer. Nice. I have an old patch which stuck this flag into page_cgroup pointer but this is of course much much better! > Signed-off-by: Johannes Weiner Acked-by: Michal Hocko Just a nit below [...] > @@ -2525,9 +2523,10 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page) memcg = NULL initialization is not needed now > VM_BUG_ON_PAGE(!PageLocked(page), page); > > pc = lookup_page_cgroup(page); > - if (PageCgroupUsed(pc)) { > - memcg = pc->mem_cgroup; > - if (memcg && !css_tryget_online(&memcg->css)) > + memcg = pc->mem_cgroup; > + > + if (memcg) { > + if (!css_tryget_online(&memcg->css)) > memcg = NULL; > } else if (PageSwapCache(page)) { > ent.val = page_private(page); > #else > static inline void memcg_unregister_all_caches(struct mem_cgroup *memcg) [...] -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/