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From: Michal Hocko <mhocko@suse.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <guro@fb.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@linux.com>,
	Shakeel Butt <shakeelb@google.com>,
	linux-mm@kvack.org, Vlastimil Babka <vbabka@suse.cz>,
	kernel-team@fb.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 05/19] mm: memcontrol: decouple reference counting from page accounting
Date: Mon, 3 Aug 2020 17:08:58 +0200	[thread overview]
Message-ID: <20200803150858.GW5174@dhcp22.suse.cz> (raw)
In-Reply-To: <20200803150349.GA502356@cmpxchg.org>

On Mon 03-08-20 11:03:49, Johannes Weiner wrote:
> On Mon, Aug 03, 2020 at 11:00:33AM +0200, Michal Hocko wrote:
> > On Tue 23-06-20 10:40:23, Roman Gushchin wrote:
> > > @@ -5456,7 +5460,10 @@ static int mem_cgroup_move_account(struct page *page,
> > >  	 */
> > >  	smp_mb();
> > >  
> > > -	page->mem_cgroup = to; 	/* caller should have done css_get */
> > > +	css_get(&to->css);
> > > +	css_put(&from->css);
> > > +
> > > +	page->mem_cgroup = to;
> > >  
> > >  	__unlock_page_memcg(from);
> > 
> > What prevents from memcg to be released here?
> 
> ->attach_task() and kill_css() are exclusive through the cgroup_mutex,
> so the base ref cannot disappear from under us during this operation.

OK, is this worth a comment? Reference counting before other operation
on the object always makes me worried and those details are hidden
elsewhere.

Btw. with the follow up fix from Hugh
Acked-by: Michal Hocko <mhocko@suse.com>
-- 
Michal Hocko
SUSE Labs


  reply	other threads:[~2020-08-03 15:09 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-23 17:40 [PATCH v7 00/19] The new cgroup slab memory controller Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 01/19] mm: memcg: factor out memcg- and lruvec-level changes out of __mod_lruvec_state() Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 02/19] mm: memcg: prepare for byte-sized vmstat items Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 03/19] mm: memcg: convert vmstat slab counters to bytes Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 04/19] mm: slub: implement SLUB version of obj_to_index() Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 05/19] mm: memcontrol: decouple reference counting from page accounting Roman Gushchin
2020-08-03  9:00   ` Michal Hocko
2020-08-03 15:03     ` Johannes Weiner
2020-08-03 15:08       ` Michal Hocko [this message]
2020-06-23 17:40 ` [PATCH v7 06/19] mm: memcg/slab: obj_cgroup API Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 07/19] mm: memcg/slab: allocate obj_cgroups for non-root slab pages Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 08/19] mm: memcg/slab: save obj_cgroup for non-root slab objects Roman Gushchin
2020-07-16 16:55   ` Naresh Kamboju
2020-07-16 20:07     ` Roman Gushchin
2020-07-17  5:34       ` Naresh Kamboju
2020-06-23 17:40 ` [PATCH v7 10/19] mm: memcg/slab: deprecate memory.kmem.slabinfo Roman Gushchin
2020-06-24  1:43   ` Shakeel Butt
2020-06-24  1:53     ` Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 11/19] mm: memcg/slab: move memcg_kmem_bypass() to memcontrol.h Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 12/19] mm: memcg/slab: use a single set of kmem_caches for all accounted allocations Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 13/19] mm: memcg/slab: simplify memcg cache creation Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 14/19] mm: memcg/slab: remove memcg_kmem_get_cache() Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 15/19] mm: memcg/slab: deprecate slab_root_caches Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 16/19] mm: memcg/slab: remove redundant check in memcg_accumulate_slabinfo() Roman Gushchin
2020-06-23 17:40 ` [PATCH v7 17/19] mm: memcg/slab: use a single set of kmem_caches for all allocations Roman Gushchin
2020-07-18 17:24   ` Guenter Roeck
2020-07-18 23:03     ` Roman Gushchin
  -- strict thread matches above, loose matches on Subject: below --
2020-06-23  1:58 [PATCH v7 00/19] The new cgroup slab memory controller Roman Gushchin
2020-06-23  1:58 ` [PATCH v7 05/19] mm: memcontrol: decouple reference counting from page accounting Roman Gushchin

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