From: Christoph Lameter <cl@linux.com>
To: Joonsoo Kim <js1304@gmail.com>
Cc: Pekka Enberg <penberg@kernel.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 3/3] slub: release a lock if freeing object with a lock is failed in __slab_free()
Date: Thu, 5 Jul 2012 09:26:50 -0500 (CDT) [thread overview]
Message-ID: <alpine.DEB.2.00.1207050924330.4138@router.home> (raw)
In-Reply-To: <1340389359-2407-3-git-send-email-js1304@gmail.com>
On Sat, 23 Jun 2012, Joonsoo Kim wrote:
> In some case of __slab_free(), we need a lock for manipulating partial list.
> If freeing object with a lock is failed, a lock doesn't needed anymore
> for some reasons.
>
> Case 1. prior is NULL, kmem_cache_debug(s) is true
>
> In this case, another free is occured before our free is succeed.
> When slab is full(prior is NULL), only possible operation is slab_free().
> So in this case, we guess another free is occured.
> It may make a slab frozen, so lock is not needed anymore.
A free cannot freeze the slab without taking the lock. The taken lock
makes sure that the thread that first enters slab_free() will be able to
hold back the thread that wants to freeze the slab.
> Case 2. inuse is NULL
>
> In this case, acquire_slab() is occured before out free is succeed.
> We have a last object for slab, so other operation for this slab is
> not possible except acquire_slab().
> Acquire_slab() makes a slab frozen, so lock is not needed anymore.
acquire_slab() also requires lock acquisition and would be held of by
slab_free holding the lock.
> This also make logic somehow simple that 'was_frozen with a lock' case
> is never occured. Remove it.
That is actually interesting and would be a good optimization.
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next prev parent reply other threads:[~2012-07-05 14:26 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <yes>
2012-06-08 17:23 ` [PATCH 1/4] slub: change declare of get_slab() to inline at all times Joonsoo Kim
2012-06-08 17:23 ` [PATCH 2/4] slub: use __cmpxchg_double_slab() at interrupt disabled place Joonsoo Kim
2012-06-08 17:23 ` [PATCH 3/4] slub: refactoring unfreeze_partials() Joonsoo Kim
2012-06-20 7:19 ` Pekka Enberg
2012-06-08 17:23 ` [PATCH 4/4] slub: deactivate freelist of kmem_cache_cpu all at once in deactivate_slab() Joonsoo Kim
2012-06-08 19:04 ` Christoph Lameter
2012-06-10 10:27 ` JoonSoo Kim
2012-06-22 18:34 ` JoonSoo Kim
2012-06-08 19:02 ` [PATCH 1/4] slub: change declare of get_slab() to inline at all times Christoph Lameter
2012-06-09 15:57 ` JoonSoo Kim
2012-06-11 15:04 ` Christoph Lameter
2012-06-22 18:22 ` [PATCH 1/3] slub: prefetch next freelist pointer in __slab_alloc() Joonsoo Kim
2012-06-22 18:22 ` [PATCH 2/3] slub: reduce failure of this_cpu_cmpxchg in put_cpu_partial() after unfreezing Joonsoo Kim
2012-07-04 13:05 ` Pekka Enberg
2012-07-05 14:20 ` Christoph Lameter
2012-08-16 7:06 ` Pekka Enberg
2012-06-22 18:22 ` [PATCH 3/3] slub: release a lock if freeing object with a lock is failed in __slab_free() Joonsoo Kim
2012-07-04 13:10 ` Pekka Enberg
2012-07-04 14:48 ` JoonSoo Kim
2012-07-05 14:26 ` Christoph Lameter [this message]
2012-07-06 14:19 ` JoonSoo Kim
2012-07-06 14:34 ` Christoph Lameter
2012-07-06 14:59 ` JoonSoo Kim
2012-07-06 15:10 ` Christoph Lameter
2012-07-08 16:19 ` JoonSoo Kim
2012-06-22 18:45 ` [PATCH 1/3 v2] slub: prefetch next freelist pointer in __slab_alloc() Joonsoo Kim
2012-07-04 12:58 ` JoonSoo Kim
2012-07-04 13:00 ` Pekka Enberg
2012-07-04 14:30 ` JoonSoo Kim
2012-07-04 15:08 ` Pekka Enberg
2012-07-04 15:26 ` Eric Dumazet
2012-07-04 15:48 ` JoonSoo Kim
2012-07-04 16:15 ` Eric Dumazet
2012-07-04 16:24 ` JoonSoo Kim
2012-07-04 15:45 ` JoonSoo Kim
2012-07-04 15:59 ` Pekka Enberg
2012-07-04 16:04 ` JoonSoo Kim
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