linux-kernel - Re: [PATCH 3/7] slub: Do not use c->page on free

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Date:	Tue, 16 Dec 2014 11:54:12 +0400
From:	Andrey Ryabinin <ryabinin.a.a@...il.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Christoph Lameter <cl@...ux.com>, akpm@...uxfoundation.org,
	rostedt@...dmis.org, LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...nel.org>,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH 3/7] slub: Do not use c->page on free

2014-12-16 5:42 GMT+03:00 Joonsoo Kim <iamjoonsoo.kim@....com>:
> On Mon, Dec 15, 2014 at 08:16:00AM -0600, Christoph Lameter wrote:
>> On Mon, 15 Dec 2014, Joonsoo Kim wrote:
>>
>> > > +static bool same_slab_page(struct kmem_cache *s, struct page *page, void *p)
>> > > +{
>> > > + long d = p - page->address;
>> > > +
>> > > + return d > 0 && d < (1 << MAX_ORDER) && d < (compound_order(page) << PAGE_SHIFT);
>> > > +}
>> > > +
>> >
>> > Somtimes, compound_order() induces one more cacheline access, because
>> > compound_order() access second struct page in order to get order. Is there
>> > any way to remove this?
>>
>> I already have code there to avoid the access if its within a MAX_ORDER
>> page. We could probably go for a smaller setting there. PAGE_COSTLY_ORDER?
>
> That is the solution to avoid compound_order() call when slab of
> object isn't matched with per cpu slab.
>
> What I'm asking is whether there is a way to avoid compound_order() call when slab
> of object is matched with per cpu slab or not.
>

Can we use page->objects for that?

Like this:

        return d > 0 && d < page->objects * s->size;
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