linux-kernel - Re: [PATCH 4/7] slub: Avoid using the page struct address in allocation fastpath

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Date:	Wed, 10 Dec 2014 18:56:33 +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 4/7] slub: Avoid using the page struct address in
 allocation fastpath

On Wed, Dec 10, 2014 at 6:30 PM, Christoph Lameter <cl@...ux.com> wrote:
> We can use virt_to_page there and only invoke the costly function if
> actually a node is specified and we have to check the NUMA locality.
>
> Increases the cost of allocating on a specific NUMA node but then that
> was never cheap since we may have to dump our caches and retrieve memory
> from the correct node.
>
> Signed-off-by: Christoph Lameter <cl@...ux.com>
>
> Index: linux/mm/slub.c
> ===================================================================
> --- linux.orig/mm/slub.c        2014-12-09 12:27:49.414686959 -0600
> +++ linux/mm/slub.c     2014-12-09 12:27:49.414686959 -0600
> @@ -2097,6 +2097,15 @@ static inline int node_match(struct page
>         return 1;
>  }
>
> +static inline int node_match_ptr(void *p, int node)
> +{
> +#ifdef CONFIG_NUMA
> +       if (!p || (node != NUMA_NO_NODE && page_to_nid(virt_to_page(p)) != node))

You already test that object != NULL before calling node_match_ptr().

> +               return 0;
> +#endif
> +       return 1;
> +}
> +
>  #ifdef CONFIG_SLUB_DEBUG
>  static int count_free(struct page *page)
>  {
> @@ -2410,7 +2419,7 @@ redo:
>
>         object = c->freelist;
>         page = c->page;
> -       if (unlikely(!object || !node_match(page, node))) {
> +       if (unlikely(!object || !node_match_ptr(object, node))) {
>                 object = __slab_alloc(s, gfpflags, node, addr, c);
>                 stat(s, ALLOC_SLOWPATH);
>         } else {
>
> --
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