linux-kernel - Re: [PATCH] mm, oom: simplify alloc_pages_before

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Date:   Fri, 1 Dec 2017 14:54:53 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Roman Gushchin <guro@...com>
Cc:     linux-mm@...r.kernel.org,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, kernel-team@...com,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm, oom: simplify alloc_pages_before_oomkill handling

On Fri 01-12-17 13:32:15, Roman Gushchin wrote:
> Hi, Michal!
> 
> I totally agree that out_of_memory() function deserves some refactoring.
> 
> But I think there is an issue with your patch (see below):
> 
> On Fri, Dec 01, 2017 at 10:14:25AM +0100, Michal Hocko wrote:
> > Recently added alloc_pages_before_oomkill gained new caller with this
> > patchset and I think it just grown to deserve a simpler code flow.
> > What do you think about this on top of the series?
> > 
> > ---
[...]
> > @@ -1112,13 +1111,8 @@ bool out_of_memory(struct oom_control *oc)
> >  	}
> >  
> >  	if (mem_cgroup_select_oom_victim(oc)) {
> > -		oc->page = alloc_pages_before_oomkill(oc);
> > -		if (oc->page) {
> > -			if (oc->chosen_memcg &&
> > -			    oc->chosen_memcg != INFLIGHT_VICTIM)
> > -				mem_cgroup_put(oc->chosen_memcg);
> 
> You're removing chosen_memcg releasing here, but I don't see where you
> do this instead. And I'm not sure that putting mem_cgroup_put() into
> alloc_pages_before_oomkill() is a way towards simpler code.

Dohh, I though I did. But obviously it is not there.

> I was thinking about a bit larger refactoring: splitting out_of_memory()
> into the following parts (defined as separate functions): victim selection
> (per-process, memcg-aware or just allocating task), last allocation attempt,
> OOM action (kill process, kill memcg, panic). Hopefully it can simplify the things,
> but I don't have code yet.

OK, I will not push if you have further plans of course. This just hit
my eyes...

-- 
Michal Hocko
SUSE Labs