linux-kernel - Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs

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Message-ID: <20171005075757.ziyj7kyzyrx7ghd6@dhcp22.suse.cz>
Date:   Thu, 5 Oct 2017 09:57:57 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Yang Shi <yang.s@...baba-inc.com>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when
 unreclaimable slabs > user memory

On Thu 05-10-17 02:08:48, Yang Shi wrote:
> 
> 
> On 10/4/17 7:27 AM, Michal Hocko wrote:
> > On Wed 04-10-17 02:06:17, Yang Shi wrote:
> > > +static bool is_dump_unreclaim_slabs(void)
> > > +{
> > > +	unsigned long nr_lru;
> > > +
> > > +	nr_lru = global_node_page_state(NR_ACTIVE_ANON) +
> > > +		 global_node_page_state(NR_INACTIVE_ANON) +
> > > +		 global_node_page_state(NR_ACTIVE_FILE) +
> > > +		 global_node_page_state(NR_INACTIVE_FILE) +
> > > +		 global_node_page_state(NR_ISOLATED_ANON) +
> > > +		 global_node_page_state(NR_ISOLATED_FILE) +
> > > +		 global_node_page_state(NR_UNEVICTABLE);
> > > +
> > > +	return (global_node_page_state(NR_SLAB_UNRECLAIMABLE) > nr_lru);
> > > +}
> > 
> > I am sorry I haven't pointed this earlier (I was following only half
> > way) but this should really be memcg aware. You are checking only global
> > counters. I do not think it is an absolute must to provide per-memcg
> > data but you should at least check !is_memcg_oom(oc).
> 
> BTW, I saw there is already such check in dump_header that looks like the
> below code:
> 
>         if (oc->memcg)
>                 mem_cgroup_print_oom_info(oc->memcg, p);
>         else
>                 show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
> 
> I'm supposed it'd better to replace "oc->memcg" to "is_memcg_oom(oc)" since
> they do the same check and "is_memcg_oom" interface sounds preferable.

Yes, is_memcg_oom is better

> Then I'm going to move unreclaimable slabs dump to the "else" block.

makes sense.
-- 
Michal Hocko
SUSE Labs