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Re: [PATCH v3 15/28] slub: always get the cache from its page in kfree [message #46576 is a reply to message #46566] Tue, 29 May 2012 15:59 Go to previous messageGo to previous message
Glauber Costa is currently offline  Glauber Costa
Messages: 916
Registered: October 2011
Senior Member
On 05/29/2012 06:42 PM, Christoph Lameter wrote:
> On Fri, 25 May 2012, Glauber Costa wrote:
>
>> struct page already have this information. If we start chaining
>> caches, this information will always be more trustworthy than
>> whatever is passed into the function
>
> Yes but the lookup of the page struct also costs some cycles. SLAB in
> !NUMA mode and SLOB avoid these lookups and can improve their freeing
> speed because of that.

But for our case, I don't really see a way around. What I can do, is
wrap it further, so when we're not using it, code goes exactly the same
way as before, instead of always calculating the page. Would it be better?

>> diff --git a/mm/slub.c b/mm/slub.c
>> index 0eb9e72..640872f 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -2598,10 +2598,14 @@ redo:
>> void kmem_cache_free(struct kmem_cache *s, void *x)
>> {
>> struct page *page;
>> + bool slab_match;
>>
>> page = virt_to_head_page(x);
>>
>> - slab_free(s, page, x, _RET_IP_);
>> + slab_match = (page->slab == s) | slab_is_parent(page->slab, s);
>> + VM_BUG_ON(!slab_match);
>
> Why add a slab_match bool if you do not really need it?

style. I find aux variables a very human readable way to deal with the
80-col limitation.
 
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