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From: Vladimir Davydov <vdavydov@parallels.com>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <akpm@linux-foundation.org>, <cl@linux.com>,
	<rientjes@google.com>, <penberg@kernel.org>, <hannes@cmpxchg.org>,
	<mhocko@suse.cz>, <linux-kernel@vger.kernel.org>,
	<linux-mm@kvack.org>
Subject: Re: [PATCH -mm v3 7/8] slub: make dead memcg caches discard free slabs immediately
Date: Tue, 24 Jun 2014 12:25:26 +0400	[thread overview]
Message-ID: <20140624082526.GD18121@esperanza> (raw)
In-Reply-To: <20140624075011.GD4836@js1304-P5Q-DELUXE>

On Tue, Jun 24, 2014 at 04:50:11PM +0900, Joonsoo Kim wrote:
> On Fri, Jun 13, 2014 at 12:38:21AM +0400, Vladimir Davydov wrote:
> > @@ -3409,6 +3417,9 @@ int __kmem_cache_shrink(struct kmem_cache *s)
> >  		kmalloc(sizeof(struct list_head) * objects, GFP_KERNEL);
> >  	unsigned long flags;
> >  
> > +	if (memcg_cache_dead(s))
> > +		s->min_partial = 0;
> > +
> >  	if (!slabs_by_inuse) {
> >  		/*
> >  		 * Do not fail shrinking empty slabs if allocation of the
> 
> I think that you should move down n->nr_partial test after holding the
> lock in __kmem_cache_shrink(). Access to n->nr_partial without node lock
> is racy and you can see wrong value. It results in skipping to free empty
> slab so your destroying logic could fail.

You're right! Will fix this.

And there seems to be the same problem in SLAB, where we check
node->slabs_free list emptiness w/o holding node->list_lock (see
drain_freelist) while it can be modified concurrently by free_block.
This will be fixed automatically after we make __kmem_cache_shrink unset
node->free_limit (which must be done under the lock) though.

Thank you!

WARNING: multiple messages have this Message-ID (diff)
From: Vladimir Davydov <vdavydov@parallels.com>
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: akpm@linux-foundation.org, cl@linux.com, rientjes@google.com,
	penberg@kernel.org, hannes@cmpxchg.org, mhocko@suse.cz,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH -mm v3 7/8] slub: make dead memcg caches discard free slabs immediately
Date: Tue, 24 Jun 2014 12:25:26 +0400	[thread overview]
Message-ID: <20140624082526.GD18121@esperanza> (raw)
In-Reply-To: <20140624075011.GD4836@js1304-P5Q-DELUXE>

On Tue, Jun 24, 2014 at 04:50:11PM +0900, Joonsoo Kim wrote:
> On Fri, Jun 13, 2014 at 12:38:21AM +0400, Vladimir Davydov wrote:
> > @@ -3409,6 +3417,9 @@ int __kmem_cache_shrink(struct kmem_cache *s)
> >  		kmalloc(sizeof(struct list_head) * objects, GFP_KERNEL);
> >  	unsigned long flags;
> >  
> > +	if (memcg_cache_dead(s))
> > +		s->min_partial = 0;
> > +
> >  	if (!slabs_by_inuse) {
> >  		/*
> >  		 * Do not fail shrinking empty slabs if allocation of the
> 
> I think that you should move down n->nr_partial test after holding the
> lock in __kmem_cache_shrink(). Access to n->nr_partial without node lock
> is racy and you can see wrong value. It results in skipping to free empty
> slab so your destroying logic could fail.

You're right! Will fix this.

And there seems to be the same problem in SLAB, where we check
node->slabs_free list emptiness w/o holding node->list_lock (see
drain_freelist) while it can be modified concurrently by free_block.
This will be fixed automatically after we make __kmem_cache_shrink unset
node->free_limit (which must be done under the lock) though.

Thank you!

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  reply	other threads:[~2014-06-24  8:25 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-06-12 20:38 [PATCH -mm v3 0/8] memcg/slab: reintroduce dead cache self-destruction Vladimir Davydov
2014-06-12 20:38 ` Vladimir Davydov
2014-06-12 20:38 ` [PATCH -mm v3 1/8] memcg: cleanup memcg_cache_params refcnt usage Vladimir Davydov
2014-06-12 20:38   ` Vladimir Davydov
2014-06-12 20:38 ` [PATCH -mm v3 2/8] memcg: destroy kmem caches when last slab is freed Vladimir Davydov
2014-06-12 20:38   ` Vladimir Davydov
2014-06-12 20:38 ` [PATCH -mm v3 3/8] memcg: mark caches that belong to offline memcgs as dead Vladimir Davydov
2014-06-12 20:38   ` Vladimir Davydov
2014-06-12 20:38 ` [PATCH -mm v3 4/8] slub: don't fail kmem_cache_shrink if slab placement optimization fails Vladimir Davydov
2014-06-12 20:38   ` Vladimir Davydov
2014-06-12 20:38 ` [PATCH -mm v3 5/8] slub: make slab_free non-preemptable Vladimir Davydov
2014-06-12 20:38   ` Vladimir Davydov
2014-06-12 20:38 ` [PATCH -mm v3 6/8] memcg: wait for kfree's to finish before destroying cache Vladimir Davydov
2014-06-12 20:38   ` Vladimir Davydov
2014-06-12 20:38 ` [PATCH -mm v3 7/8] slub: make dead memcg caches discard free slabs immediately Vladimir Davydov
2014-06-12 20:38   ` Vladimir Davydov
2014-06-13 16:54   ` Christoph Lameter
2014-06-13 16:54     ` Christoph Lameter
2014-06-24  7:50   ` Joonsoo Kim
2014-06-24  7:50     ` Joonsoo Kim
2014-06-24  8:25     ` Vladimir Davydov [this message]
2014-06-24  8:25       ` Vladimir Davydov
2014-06-24  9:42     ` [PATCH -mm] slub: kmem_cache_shrink: check if partial list is empty under list_lock Vladimir Davydov
2014-06-24  9:42       ` Vladimir Davydov
2014-06-12 20:38 ` [PATCH -mm v3 8/8] slab: do not keep free objects/slabs on dead memcg caches Vladimir Davydov
2014-06-12 20:38   ` Vladimir Davydov
2014-06-12 20:41   ` Vladimir Davydov
2014-06-12 20:41     ` Vladimir Davydov
2014-06-24  7:25   ` Joonsoo Kim
2014-06-24  7:25     ` Joonsoo Kim
2014-06-24  7:42     ` Vladimir Davydov
2014-06-24  7:42       ` Vladimir Davydov
2014-06-24 12:28     ` [PATCH -mm] slab: set free_limit for dead caches to 0 Vladimir Davydov
2014-06-24 12:28       ` Vladimir Davydov
2014-06-24  7:38   ` [PATCH -mm v3 8/8] slab: do not keep free objects/slabs on dead memcg caches Joonsoo Kim
2014-06-24  7:38     ` Joonsoo Kim
2014-06-24  7:48     ` Vladimir Davydov
2014-06-24  7:48       ` Vladimir Davydov
2014-06-25 13:45     ` Vladimir Davydov
2014-06-25 13:45       ` Vladimir Davydov
2014-06-27  6:05       ` Joonsoo Kim
2014-06-27  6:05         ` Joonsoo Kim
2014-06-30 15:49         ` Christoph Lameter
2014-06-30 15:49           ` Christoph Lameter
2014-07-01  7:46           ` Vladimir Davydov
2014-07-01  7:46             ` Vladimir Davydov
2014-06-25 14:39     ` [PATCH] slab: document why cache can have no per cpu array on kfree Vladimir Davydov
2014-06-25 14:39       ` Vladimir Davydov
2014-06-25 16:19       ` Christoph Lameter
2014-06-25 16:19         ` Christoph Lameter

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