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

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Message-ID: <CAOJsxLH4BGT9rGgg_4nxUMgW3sdEzLrmX2WtM8Ld3aytdR5e8g@mail.gmail.com>
Date:	Wed, 10 Dec 2014 19:32:25 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	akpm <akpm@...uxfoundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, iamjoonsoo@....com,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH 3/7] slub: Do not use c->page on free

On Wed, Dec 10, 2014 at 7:08 PM, Christoph Lameter <cl@...ux.com> wrote:
>> > +{
>> > +       long d = p - page->address;
>> > +
>> > +       return d > 0 && d < (1 << MAX_ORDER) && d < (compound_order(page) << PAGE_SHIFT);
>> > +}
>>
>> Can you elaborate on what this is doing? I don't really understand it.
>
> Checks if the pointer points to the slab page. Also it tres to avoid
> having to call compound_order needlessly. Not sure if that optimization is
> worth it.

Aah, it's the (1 << MAX_ORDER) optimization that confused me. Perhaps
add a comment there to make it more obvious?

I'm fine with the optimization:

Reviewed-by: Pekka Enberg <penberg@...nel.org>

- Pekka
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