From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id 4F62E6B0038 for ; Fri, 15 Sep 2017 14:45:01 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id b195so3861952wmb.6 for ; Fri, 15 Sep 2017 11:45:01 -0700 (PDT) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id 7si1669809edj.524.2017.09.15.11.44.59 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 15 Sep 2017 11:45:00 -0700 (PDT) Date: Fri, 15 Sep 2017 11:44:49 -0700 From: Johannes Weiner Subject: Re: [PATCH] mm,page_alloc: softlockup on warn_alloc on Message-ID: <20170915184449.GA9859@cmpxchg.org> References: <20170915095849.9927-1-yuwang668899@gmail.com> <20170915143732.GA8397@cmpxchg.org> <201709160023.CAE05229.MQHFSJFOOFOVtL@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201709160023.CAE05229.MQHFSJFOOFOVtL@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: yuwang668899@gmail.com, mhocko@suse.com, linux-mm@kvack.org, chenggang.qcg@alibaba-inc.com, yuwang.yuwang@alibaba-inc.com, akpm@linux-foundation.org On Sat, Sep 16, 2017 at 12:23:53AM +0900, Tetsuo Handa wrote: > Johannes Weiner wrote: > > How can we figure out if there is a bug here? Can we time the calls to > > __alloc_pages_direct_reclaim() and __alloc_pages_direct_compact() and > > drill down from there? Print out the number of times we have retried? > > We're counting no_progress_loops, but we are also very much interested > > in progress_loops that didn't result in a successful allocation. Too > > many of those and I think we want to OOM kill as per above. > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index bec5e96f3b88..01736596389a 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -3830,6 +3830,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > > "page allocation stalls for %ums, order:%u", > > jiffies_to_msecs(jiffies-alloc_start), order); > > stall_timeout += 10 * HZ; > > + goto oom; > > } > > > > /* Avoid recursion of direct reclaim */ > > @@ -3882,6 +3883,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > > if (read_mems_allowed_retry(cpuset_mems_cookie)) > > goto retry_cpuset; > > > > +oom: > > /* Reclaim has failed us, start killing things */ > > page = __alloc_pages_may_oom(gfp_mask, order, ac, &did_some_progress); > > if (page) > > > > According to my stress tests, it is mutex_trylock() in __alloc_pages_may_oom() > that causes warn_alloc() to be called for so many times. The comment > > /* > * Acquire the oom lock. If that fails, somebody else is > * making progress for us. > */ > > is true only if the owner of oom_lock can call out_of_memory() and is __GFP_FS > allocation. Consider a situation where there are 1 GFP_KERNEL allocating thread > and 99 GFP_NOFS/GFP_NOIO allocating threads contending the oom_lock. How likely > the OOM killer is invoked? It is very unlikely because GFP_KERNEL allocating thread > likely fails to grab oom_lock because GFP_NOFS/GFP_NOIO allocating threads is > grabing oom_lock. And GFP_KERNEL allocating thread yields CPU time for > GFP_NOFS/GFP_NOIO allocating threads to waste pointlessly. > s/!mutex_trylock(&oom_lock)/mutex_lock_killable()/ significantly improves > this situation for my stress tests. How is your case? Interesting analysis, that definitely sounds plausible. It just started happening to us in production and I haven't isolated it yet. If you already have a reproducer, that's excellent. The synchronization has worked this way for a long time (trylock failure assuming progress, but the order/NOFS/zone bailouts from actually OOM-killing inside the locked section). We should really fix *that* rather than serializing warn_alloc(). For GFP_NOFS, it seems to go back to 9879de7373fc ("mm: page_alloc: embed OOM killing naturally into allocation slowpath"). Before that we didn't use to call __alloc_pages_may_oom() for NOFS allocations. So I still wonder why this only now appears to be causing problems. In any case, converting that trylock to a sleeping lock in this case makes sense to me. Nobody is blocking under this lock (except that one schedule_timeout_killable(1) after dispatching a victim) and it's not obvious to me why we'd need that level of concurrency under OOM. -- 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