Re: [PATCH 2/2] slab: move kmem_cache_free to common code
From: Glauber Costa
Date: Tue Oct 23 2012 - 04:07:21 EST
On 10/23/2012 04:48 AM, JoonSoo Kim wrote:
> Hello, Glauber.
> 2012/10/23 Glauber Costa <glommer@xxxxxxxxxxxxx>:
>> 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);
>>> 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.
Ah, this. Ok, I got fooled by his mention to tracing.
I do agree, but since freeing is ultimately dependent on the allocator
layout, I don't see a clean way of doing this without dropping tears of
sorrow around. The calls in slub/slab/slob would have to be somehow
inlined. Hum... maybe it is possible to do it from
Let me give it a try and see what I can come up with.
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