linux-kernel - Re: [patch 5/7] mm: page_cgroup: check page_cgroup arrays in lookup_page

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Date:	Wed, 30 Nov 2011 08:42:11 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 5/7] mm: page_cgroup: check page_cgroup arrays in
 lookup_page_cgroup() only when necessary

On Tue, 29 Nov 2011 11:52:03 +0100
Johannes Weiner <hannes@...xchg.org> wrote:

> lookup_page_cgroup() is usually used only against pages that are used
> in userspace.
> 
> The exception is the CONFIG_DEBUG_VM-only memcg check from the page
> allocator: it can run on pages without page_cgroup descriptors
> allocated when the pages are fed into the page allocator for the first
> time during boot or memory hotplug.
> 
> Include the array check only when CONFIG_DEBUG_VM is set and save the
> unnecessary check in production kernels.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>


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