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

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Date:	Wed, 10 Dec 2014 18:54:47 +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 6:30 PM, Christoph Lameter <cl@...ux.com> wrote:
> Avoid using the page struct address on free by just doing an
> address comparison. That is easily doable now that the page address
> is available in the page struct and we already have the page struct
> address of the object to be freed calculated.
>
> Signed-off-by: Christoph Lameter <cl@...ux.com>
>
> Index: linux/mm/slub.c
> ===================================================================
> --- linux.orig/mm/slub.c        2014-12-09 12:25:45.770405462 -0600
> +++ linux/mm/slub.c     2014-12-09 12:25:45.766405582 -0600
> @@ -2625,6 +2625,13 @@ slab_empty:
>         discard_slab(s, page);
>  }
>
> +static bool same_slab_page(struct kmem_cache *s, struct page *page, void *p)

Why are you passing a pointer to struct kmem_cache here? You don't
seem to use it.

> +{
> +       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.

- Pekka
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