From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932447AbaLDPSE (ORCPT ); Thu, 4 Dec 2014 10:18:04 -0500 Received: from mail-wi0-f181.google.com ([209.85.212.181]:40700 "EHLO mail-wi0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932094AbaLDPSC (ORCPT ); Thu, 4 Dec 2014 10:18:02 -0500 Date: Thu, 4 Dec 2014 16:17:58 +0100 From: Michal Hocko To: Johannes Weiner Cc: David Rientjes , Andrew Morton , Qiang Huang , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch] mm, oom: remove gfp helper function Message-ID: <20141204151758.GC25001@dhcp22.suse.cz> References: <20141127102547.GA18833@dhcp22.suse.cz> <20141201233040.GB29642@phnom.home.cmpxchg.org> <20141203155222.GH23236@dhcp22.suse.cz> <20141203181509.GA24567@phnom.home.cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141203181509.GA24567@phnom.home.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 Wed 03-12-14 13:15:09, Johannes Weiner wrote: > On Wed, Dec 03, 2014 at 04:52:22PM +0100, Michal Hocko wrote: > > On Mon 01-12-14 18:30:40, Johannes Weiner wrote: > > > On Thu, Nov 27, 2014 at 11:25:47AM +0100, Michal Hocko wrote: > > > > On Wed 26-11-14 14:17:32, David Rientjes wrote: > > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > > > > --- a/mm/page_alloc.c > > > > > +++ b/mm/page_alloc.c > > > > > @@ -2706,7 +2706,7 @@ rebalance: > > > > > * running out of options and have to consider going OOM > > > > > */ > > > > > if (!did_some_progress) { > > > > > - if (oom_gfp_allowed(gfp_mask)) { > > > > /* > > > > * Do not attempt to trigger OOM killer for !__GFP_FS > > > > * allocations because it would be premature to kill > > > > * anything just because the reclaim is stuck on > > > > * dirty/writeback pages. > > > > * __GFP_NORETRY allocations might fail and so the OOM > > > > * would be more harmful than useful. > > > > */ > > > > > > I don't think we need to explain the individual flags, but it would > > > indeed be useful to remark here that we shouldn't OOM kill from > > > allocations contexts with (severely) limited reclaim abilities. > > > > Is __GFP_NORETRY really related to limited reclaim abilities? I thought > > it was merely a way to tell the allocator to fail rather than spend too > > much time reclaiming. > > And you wouldn't call that "limited reclaim ability"? I really do not want to go into language lawyering here. But to me the reclaim ability is what the reclaim is capable to do with the given gfp. And __GFP_NORETRY is completely irrelevant for the reclaim. It tells the allocator how hard it should try (similar like __GFP_REPEAT or __GFP_NOFAIL) unlike __GFP_FS which restricts the reclaim in its operation. > I guess it's a > matter of phrasing, but the point is that we don't want anybody to OOM > kill that didn't exhaust all other options that are usually available > to allocators. This includes the ability to enter the FS, the ability > to do IO in general, and the ability to retry reclaim. Possibly more. Right. > > If you are referring to __GFP_FS part then I have > > no objections to be less specific, of course, but __GFP_IO would fall > > into the same category but we are not checking for it. I have no idea > > why we consider the first and not the later one, to be honest... > > Which proves my point that we should document high-level intent rather > than implementation. Suddenly, that missing __GFP_IO is sticking out > like a sore thumb... I am obviously not insisting on the above wording. I am for everything that would clarify the test and do not force me to go through several hops of the git blame to find the original intention again after year when I forget this again. -- Michal Hocko SUSE Labs