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

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Message-ID: <20141215080338.GE4898@js1304-P5Q-DELUXE>
Date:	Mon, 15 Dec 2014 17:03:38 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	akpm@...uxfoundation.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	linux-mm@...ck.org, penberg@...nel.org,
	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 10:30:20AM -0600, Christoph Lameter 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)
> +{
> +	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?

Thanks.

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