linux-kernel - Re: [PATCH v2 07/11] mm: Allocate kernel pages to the right memcg

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Message-ID: <20120815092404.GA23985@dhcp22.suse.cz>
Date:	Wed, 15 Aug 2012 11:24:05 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org, devel@...nvz.org,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	kamezawa.hiroyu@...fujitsu.com, Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH v2 07/11] mm: Allocate kernel pages to the right memcg

On Thu 09-08-12 17:01:15, Glauber Costa wrote:
[...]
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b956cec..da341dc 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2532,6 +2532,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>  	struct page *page = NULL;
>  	int migratetype = allocflags_to_migratetype(gfp_mask);
>  	unsigned int cpuset_mems_cookie;
> +	void *handle = NULL;
>  
>  	gfp_mask &= gfp_allowed_mask;
>  
> @@ -2543,6 +2544,13 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>  		return NULL;
>  
>  	/*
> +	 * Will only have any effect when __GFP_KMEMCG is set.
> +	 * This is verified in the (always inline) callee
> +	 */
> +	if (!memcg_kmem_new_page(gfp_mask, &handle, order))
> +		return NULL;

When the previous patch introduced this function I thought the handle
obfuscantion is to prevent from spreading struct mem_cgroup inside the
page allocator but memcg_kmem_commit_page uses the type directly. So why
that obfuscation? Even handle as a name sounds unnecessarily confusing.
I would go with struct mem_cgroup **memcgp or even return the pointer on
success or NULL otherwise.

[...]
> +EXPORT_SYMBOL(__free_accounted_pages);

Why exported?

Btw. this is called from call_rcu context but it itself calls call_rcu
down the chain in mem_cgroup_put. Is it safe?

[...]
> +EXPORT_SYMBOL(free_accounted_pages);

here again
-- 
Michal Hocko
SUSE Labs
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