linux-kernel - Re: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at should_reclaim

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Message-ID: <20180905140451.GG14951@dhcp22.suse.cz>
Date:   Wed, 5 Sep 2018 16:04:51 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     David Rientjes <rientjes@...gle.com>, Tejun Heo <tj@...nel.org>,
        Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at
 should_reclaim_retry().

On Wed 05-09-18 22:53:33, Tetsuo Handa wrote:
> On 2018/09/05 22:40, Michal Hocko wrote:
> > Changelog said 
> > 
> > "Although this is possible in principle let's wait for it to actually
> > happen in real life before we make the locking more complex again."
> > 
> > So what is the real life workload that hits it? The log you have pasted
> > below doesn't tell much.
> 
> Nothing special. I just ran a multi-threaded memory eater on a CONFIG_PREEMPT=y kernel.

I strongly suspec that your test doesn't really represent or simulate
any real and useful workload. Sure it triggers a rare race and we kill
another oom victim. Does this warrant to make the code more complex?
Well, I am not convinced, as I've said countless times.
-- 
Michal Hocko
SUSE Labs