From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id BD05E6B026B for ; Mon, 25 Jun 2018 10:12:48 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id i10-v6so2369593eds.19 for ; Mon, 25 Jun 2018 07:12:48 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id c4-v6si891771edf.296.2018.06.25.07.12.47 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 25 Jun 2018 07:12:47 -0700 (PDT) Date: Mon, 25 Jun 2018 16:12:46 +0200 From: Michal Hocko Subject: Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer. Message-ID: <20180625141246.GN28965@dhcp22.suse.cz> References: <1529493638-6389-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20180620115531.GL13685@dhcp22.suse.cz> <3d27f26e-68ba-d3c0-9518-cebeb2689aec@sony.com> <20180625130756.GK28965@dhcp22.suse.cz> <9a14d554-6470-e0d6-19cc-1ecec17a47c7@sony.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9a14d554-6470-e0d6-19cc-1ecec17a47c7@sony.com> Sender: owner-linux-mm@kvack.org List-ID: To: peter enderborg Cc: Tetsuo Handa , linux-mm@kvack.org, rientjes@google.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org On Mon 25-06-18 16:04:04, peter enderborg wrote: > On 06/25/2018 03:07 PM, Michal Hocko wrote: > > > On Mon 25-06-18 15:03:40, peter enderborg wrote: > >> On 06/20/2018 01:55 PM, Michal Hocko wrote: > >>> On Wed 20-06-18 20:20:38, Tetsuo Handa wrote: > >>>> Sleeping with oom_lock held can cause AB-BA lockup bug because > >>>> __alloc_pages_may_oom() does not wait for oom_lock. Since > >>>> blocking_notifier_call_chain() in out_of_memory() might sleep, sleeping > >>>> with oom_lock held is currently an unavoidable problem. > >>> Could you be more specific about the potential deadlock? Sleeping while > >>> holding oom lock is certainly not nice but I do not see how that would > >>> result in a deadlock assuming that the sleeping context doesn't sleep on > >>> the memory allocation obviously. > >> It is a mutex you are supposed to be able to sleep.A It's even exported. > > What do you mean? oom_lock is certainly not exported for general use. It > > is not local to oom_killer.c just because it is needed in other _mm_ > > code. > > > > ItA is in the oom.h file include/linux/oom.h, if it that sensitive it should > be in mm/ and a documented note about the special rules. It is only used > in drivers/tty/sysrq.c and that be replaced by a help function in mm that > do theA oom stuff. Well, there are many things defined in kernel header files and not meant for wider use. Using random locks is generally discouraged I would say unless you are sure you know what you are doing. We could do some more work to hide internals for sure, though. > >>>> As a preparation for not to sleep with oom_lock held, this patch brings > >>>> OOM notifier callbacks to outside of OOM killer, with two small behavior > >>>> changes explained below. > >>> Can we just eliminate this ugliness and remove it altogether? We do not > >>> have that many notifiers. Is there anything fundamental that would > >>> prevent us from moving them to shrinkers instead? > >> @Hocko Do you remember the lowmemorykiller from android? Some things > >> might not be the right thing for shrinkers. > > Just that lmk did it wrong doesn't mean others have to follow. > > > If all you have is a hammer, everything looks like a nail. (I dona??t argument that it was right) > But if you dona??t have a way to interact with the memory system we will get attempts like lmk.A > Oom notifiers and vmpressure is for this task better than shrinkers. A lack of feature should be a trigger for a discussion rather than a quick hack that seems to work for a particular usecase and live out of tree, then get to staging and hope it will fix itself. Seriously, the kernel development is not a nail hammering. -- Michal Hocko SUSE Labs