linux-kernel - Re: [patch -mm] mm, memcg: evaluate root and leaf memcgs fairly on oom

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Date:   Wed, 14 Mar 2018 13:41:03 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Roman Gushchin <guro@...com>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch -mm] mm, memcg: evaluate root and leaf memcgs fairly on
 oom

On Wed, 14 Mar 2018, Roman Gushchin wrote:

> > @@ -2618,92 +2620,65 @@ static long memcg_oom_badness(struct mem_cgroup *memcg,
> >  		if (nodemask && !node_isset(nid, *nodemask))
> >  			continue;
> >  
> > -		points += mem_cgroup_node_nr_lru_pages(memcg, nid,
> > -				LRU_ALL_ANON | BIT(LRU_UNEVICTABLE));
> > -
> >  		pgdat = NODE_DATA(nid);
> > -		points += lruvec_page_state(mem_cgroup_lruvec(pgdat, memcg),
> > -					    NR_SLAB_UNRECLAIMABLE);
> > +		if (is_root_memcg) {
> > +			points += node_page_state(pgdat, NR_ACTIVE_ANON) +
> > +				  node_page_state(pgdat, NR_INACTIVE_ANON);
> > +			points += node_page_state(pgdat, NR_SLAB_UNRECLAIMABLE);
> > +		} else {
> > +			points += mem_cgroup_node_nr_lru_pages(memcg, nid,
> > +							       LRU_ALL_ANON);
> > +			points += lruvec_page_state(mem_cgroup_lruvec(pgdat, memcg),
> > +						    NR_SLAB_UNRECLAIMABLE);
> > +		}
> >  	}
> >  
> > -	points += memcg_page_state(memcg, MEMCG_KERNEL_STACK_KB) /
> > -		(PAGE_SIZE / 1024);
> > -	points += memcg_page_state(memcg, MEMCG_SOCK);
> > -	points += memcg_page_state(memcg, MEMCG_SWAP);
> > -
> > +	if (is_root_memcg) {
> > +		points += global_zone_page_state(NR_KERNEL_STACK_KB) /
> > +				(PAGE_SIZE / 1024);
> > +		points += atomic_long_read(&total_sock_pages);
>                                             ^^^^^^^^^^^^^^^^
> BTW, where do we change this counter?
> 

Seems like it was dropped from the patch somehow.  It is intended to do 
atomic_long_add(nr_pages) in mem_cgroup_charge_skmem() and 
atomic_long_add(-nr_pages) mem_cgroup_uncharge_skmem().

> I also doubt that global atomic variable can work here,
> we probably need something better scaling.
> 

Why do you think an atomic_long_add() is too expensive when we're already 
disabling irqs and dong try_charge()?