Re: [PATCH v3 15/28] slub: always get the cache from its page inkfree

[Glauber Costa]

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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