linux-kernel - Re: [PATCH v2] mm/slub: don't wait for high-order page allocation

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Message-ID: <20150807150501.GJ30785@dhcp22.suse.cz>
Date:	Fri, 7 Aug 2015 17:05:01 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Joonsoo Kim <js1304@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>, Shaohua Li <shli@...com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v2] mm/slub: don't wait for high-order page allocation

On Fri 07-08-15 11:10:03, Joonsoo Kim wrote:
[...]
> diff --git a/mm/slub.c b/mm/slub.c
> index 257283f..52b9025 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1364,6 +1364,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
>  	 * so we fall-back to the minimum order allocation.
>  	 */
>  	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL;
> +	if ((alloc_gfp & __GFP_WAIT) && oo_order(oo) > oo_order(s->min))
> +		alloc_gfp = (alloc_gfp | __GFP_NOMEMALLOC) & ~__GFP_WAIT;

Wouldn't it be preferable to "fix" the __GFP_WAIT behavior than spilling
__GFP_NOMEMALLOC around the kernel? GFP flags are getting harder and
harder to use right and that is a signal we should thing about it and
unclutter the current state.

>  
>  	page = alloc_slab_page(s, alloc_gfp, node, oo);
>  	if (unlikely(!page)) {
> -- 
> 1.9.1

-- 
Michal Hocko
SUSE Labs
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