linux-kernel - Re: [patch] mm, slab: only set __GFP

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Date:   Wed, 18 Oct 2017 14:54:02 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Christoph Lameter <cl@...ux.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [patch] mm, slab: only set __GFP_RECLAIMABLE once

+CC Mel who added that code (long time ago though :) in case he
remembers some catch.

On 10/18/2017 12:30 AM, David Rientjes wrote:
> SLAB_RECLAIM_ACCOUNT is a permanent attribute of a slab cache.  Set 
> __GFP_RECLAIMABLE as part of its ->allocflags rather than check the cachep 
> flag on every page allocation.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>

Seems correct to me, and SLUB does that this way too, since the beginning.

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/slab.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/slab.c b/mm/slab.c
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1409,8 +1409,6 @@ static struct page *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
>  	int nr_pages;
>  
>  	flags |= cachep->allocflags;
> -	if (cachep->flags & SLAB_RECLAIM_ACCOUNT)
> -		flags |= __GFP_RECLAIMABLE;
>  
>  	page = __alloc_pages_node(nodeid, flags | __GFP_NOTRACK, cachep->gfporder);
>  	if (!page) {
> @@ -2143,6 +2141,8 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
>  	cachep->allocflags = __GFP_COMP;
>  	if (flags & SLAB_CACHE_DMA)
>  		cachep->allocflags |= GFP_DMA;
> +	if (flags & SLAB_RECLAIM_ACCOUNT)
> +		cachep->allocflags |= __GFP_RECLAIMABLE;
>  	cachep->size = size;
>  	cachep->reciprocal_buffer_size = reciprocal_value(size);
>  
> 
> --
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