linux-kernel - Re: [PATCH 2/2] slab: move kmem_cache

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Date:	Tue, 23 Oct 2012 09:48:19 +0900
From:	JoonSoo Kim <js1304@...il.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Christoph Lameter <cl@...ux.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 2/2] slab: move kmem_cache_free to common code

Hello, Glauber.

2012/10/23 Glauber Costa <glommer@...allels.com>:
> On 10/22/2012 06:45 PM, Christoph Lameter wrote:
>> On Mon, 22 Oct 2012, Glauber Costa wrote:
>>
>>> + * kmem_cache_free - Deallocate an object
>>> + * @cachep: The cache the allocation was from.
>>> + * @objp: The previously allocated object.
>>> + *
>>> + * Free an object which was previously allocated from this
>>> + * cache.
>>> + */
>>> +void kmem_cache_free(struct kmem_cache *s, void *x)
>>> +{
>>> +    __kmem_cache_free(s, x);
>>> +    trace_kmem_cache_free(_RET_IP_, x);
>>> +}
>>> +EXPORT_SYMBOL(kmem_cache_free);
>>> +
>>
>> This results in an additional indirection if tracing is off. Wonder if
>> there is a performance impact?
>>
> if tracing is on, you mean?
>
> Tracing already incurs overhead, not sure how much a function call would
> add to the tracing overhead.
>
> I would not be concerned with this, but I can measure, if you have any
> specific workload in mind.

With this patch, kmem_cache_free() invokes __kmem_cache_free(),
that is, it add one more "call instruction" than before.

I think that Christoph's comment means above fact.

Thanks.
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