From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 622AF6B025E for ; Tue, 6 Dec 2016 06:03:21 -0500 (EST) Received: by mail-wm0-f69.google.com with SMTP id a20so24075648wme.5 for ; Tue, 06 Dec 2016 03:03:21 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id f184si3137431wme.33.2016.12.06.03.03.19 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 06 Dec 2016 03:03:19 -0800 (PST) Subject: Re: [PATCH 2/2] mm, oom: do not enfore OOM killer for __GFP_NOFAIL automatically References: <20161201152517.27698-1-mhocko@kernel.org> <20161201152517.27698-3-mhocko@kernel.org> <201612052245.HDB21880.OHJMOOQFFSVLtF@I-love.SAKURA.ne.jp> <20161205141009.GJ30758@dhcp22.suse.cz> <201612061938.DDD73970.QFHOFJStFOLVOM@I-love.SAKURA.ne.jp> From: Vlastimil Babka Message-ID: <01a495b8-36f6-28f5-5a55-089f4860747d@suse.cz> Date: Tue, 6 Dec 2016 12:03:02 +0100 MIME-Version: 1.0 In-Reply-To: <201612061938.DDD73970.QFHOFJStFOLVOM@I-love.SAKURA.ne.jp> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa , mhocko@kernel.org Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mgorman@suse.de, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 12/06/2016 11:38 AM, Tetsuo Handa wrote: >> >> So we are somewhere in the middle between pre-mature and pointless >> system disruption (GFP_NOFS with a lots of metadata or lowmem request) >> where the OOM killer even might not help and potential lockup which is >> inevitable with the current design. Dunno about you but I would rather >> go with the first option. To be honest I really fail to understand your >> line of argumentation. We have this >> do { >> cond_resched(); >> } while (!(page = alloc_page(GFP_NOFS))); >> vs. >> page = alloc_page(GFP_NOFS | __GFP_NOFAIL); >> >> the first one doesn't invoke OOM killer while the later does. This >> discrepancy just cannot make any sense... The same is true for >> >> alloc_page(GFP_DMA) vs alloc_page(GFP_DMA|__GFP_NOFAIL) >> >> Now we can discuss whether it is a _good_ idea to not invoke OOM killer >> for those exceptions but whatever we do __GFP_NOFAIL is not a way to >> give such a subtle side effect. Or do you disagree even with that? > > "[PATCH 1/2] mm: consolidate GFP_NOFAIL checks in the allocator slowpath" > silently changes __GFP_NOFAIL vs. __GFP_NORETRY priority. I guess that wasn't intended? > Currently, __GFP_NORETRY is stronger than __GFP_NOFAIL; __GFP_NOFAIL > allocation requests fail without invoking the OOM killer when both > __GFP_NORETRY and __GFP_NOFAIL are given. > > With [PATCH 1/2], __GFP_NOFAIL becomes stronger than __GFP_NORETRY; > __GFP_NOFAIL allocation requests will loop forever without invoking > the OOM killer when both __GFP_NORETRY and __GFP_NOFAIL are given. Does such combination of flag make sense? Should we warn about it, or even silently remove __GFP_NORETRY in such case? > Those callers which prefer lockup over panic can specify both > __GFP_NORETRY and __GFP_NOFAIL. What lockup exactly, if __GFP_NORETRY did lead to fail? -- 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