linux-kernel - Re: [RFC PATCH] page_cgroup: Reduce allocation overhead for page_cgroup array for CONFIG

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Message-Id: <20110224085227.1a3e185b.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 24 Feb 2011 08:52:27 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] page_cgroup: Reduce allocation overhead for
 page_cgroup array for CONFIG_SPARSEMEM

On Wed, 23 Feb 2011 10:19:22 -0800
Dave Hansen <dave@...ux.vnet.ibm.com> wrote:

> On Wed, 2011-02-23 at 16:10 +0100, Michal Hocko wrote:
> > We can reduce this internal fragmentation by splitting the single
> > page_cgroup array into more arrays where each one is well kmalloc
> > aligned. This patch implements this idea. 
> 
> How about using alloc_pages_exact()?  These things aren't allocated
> often enough to really get most of the benefits of being in a slab.
> That'll at least get you down to a maximum of about PAGE_SIZE wasted.  
> 

yes, alloc_pages_exact() is much better.

packing page_cgroups for multiple sections causes breakage in memory hotplug logic.

Thanks,
-Kame

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