linux-kernel - Re: [PATCH 09/16] slab: use __GFP_COMP flag for allocating slab pages

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Message-ID: <00000140a72fb556-3269e81c-8829-4c26-a57f-c1bb7e40977b-000000@email.amazonses.com>
Date:	Thu, 22 Aug 2013 18:00:56 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
cc:	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <js1304@...il.com>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/16] slab: use __GFP_COMP flag for allocating slab
 pages

On Thu, 22 Aug 2013, Joonsoo Kim wrote:

> If we use 'struct page' of first page as 'struct slab', there is no
> advantage not to use __GFP_COMP. So use __GFP_COMP flag for all the cases.

Ok that brings it in line with SLUB and SLOB.

> @@ -2717,17 +2701,8 @@ static void slab_put_obj(struct kmem_cache *cachep, struct slab *slabp,
>  static void slab_map_pages(struct kmem_cache *cache, struct slab *slab,
>  			   struct page *page)
>  {
> -	int nr_pages;
> -
> -	nr_pages = 1;
> -	if (likely(!PageCompound(page)))
> -		nr_pages <<= cache->gfporder;
> -
> -	do {
> -		page->slab_cache = cache;
> -		page->slab_page = slab;
> -		page++;
> -	} while (--nr_pages);
> +	page->slab_cache = cache;
> +	page->slab_page = slab;
>  }

And saves some processing.

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