Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759305Ab1FWNBn (ORCPT ); Thu, 23 Jun 2011 09:01:43 -0400 Received: from mail-bw0-f46.google.com ([209.85.214.46]:53571 "EHLO mail-bw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758942Ab1FWNBm (ORCPT ); Thu, 23 Jun 2011 09:01:42 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; b=VsYoDhTTw1UxUSqIIwMvMXLEKVAJLvQu5GMiJ17/alvqus/EHLcho3ZQTethi3K8kV UTdGf3IcyS4blcvmzYStyhfQiZtEJPZLpLjQyLjkX4itCLprpKKMc2cieZopDGtjkoKy fU3X1uOamhIqOxrfegMan7pJNJaShDNZp92bI= MIME-Version: 1.0 In-Reply-To: <20110623115855.GF31593@tiehlicka.suse.cz> References: <20110622120635.GB14343@tiehlicka.suse.cz> <20110622121516.GA28359@infradead.org> <20110622123204.GC14343@tiehlicka.suse.cz> <20110623150842.d13492cd.kamezawa.hiroyu@jp.fujitsu.com> <20110623074133.GA31593@tiehlicka.suse.cz> <20110623170811.16f4435f.kamezawa.hiroyu@jp.fujitsu.com> <20110623090204.GE31593@tiehlicka.suse.cz> <20110623190157.1bc8cbb9.kamezawa.hiroyu@jp.fujitsu.com> <20110623115855.GF31593@tiehlicka.suse.cz> Date: Thu, 23 Jun 2011 22:01:40 +0900 Message-ID: Subject: Re: [PATCH] mm: preallocate page before lock_page at filemap COW. (WasRe: [PATCH V2] mm: Do not keep page locked during page fault while charging it for memcg From: Hiroyuki Kamezawa To: Michal Hocko Cc: KAMEZAWA Hiroyuki , Christoph Hellwig , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Hugh Dickins , Rik van Riel , Michel Lespinasse , Mel Gorman , Lutz Vieweg Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2164 Lines: 60 2011/6/23 Michal Hocko : > On Thu 23-06-11 19:01:57, KAMEZAWA Hiroyuki wrote: >> On Thu, 23 Jun 2011 11:02:04 +0200 >> Michal Hocko wrote: >> >> > On Thu 23-06-11 17:08:11, KAMEZAWA Hiroyuki wrote: >> > > On Thu, 23 Jun 2011 09:41:33 +0200 >> > > Michal Hocko wrote: >> > [...] >> > > > Other than that: >> > > > Reviewed-by: Michal Hocko >> > > > >> > > >> > > I found the page is added to LRU before charging. (In this case, >> > > memcg's LRU is ignored.) I'll post a new version with a fix. >> > >> > Yes, you are right. I have missed that. >> > This means that we might race with reclaim which could evict the COWed >> > page wich in turn would uncharge that page even though we haven't >> > charged it yet. >> > >> > Can we postpone page_add_new_anon_rmap to the charging path or it would >> > just race somewhere else? >> > >> >> I got a different idea. How about this ? >> I think this will have benefit for non-memcg users under OOM, too. > > Could you be more specific? I do not see how preallocation which might > turn out to be pointless could help under OOM. > We'll have no page allocation under lock_page() held in this path. I think it is good. >> >> A concerns is VM_FAULT_RETRY case but wait-for-lock will be much heavier >> than preallocation + free-for-retry cost. > > Preallocation is rather costly when fault handler fails (e.g. SIGBUS > which is the easiest one to trigger). > I think pcp cache of free page allocater does enough good job and I guess we'll see no problem even if there is a storm of SIGBUS. > I am not saying this approach is bad but I think that preallocation can > be much more costly than unlock, charge and lock&recheck approach. memcg_is_disabled() cannot help ROOT cgroup. And additional lock/unlock method may kill FAULT_RETRY at lock contention optimization which was added recently. Thanks, -Kame -- 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/