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

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Message-ID: <20110224093519.GB20922@tiehlicka.suse.cz>
Date:	Thu, 24 Feb 2011 10:35:19 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>, 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 Thu 24-02-11 08:52:27, KAMEZAWA Hiroyuki wrote:
> 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.

I am not sure I understand this. What do you mean by packing
page_cgroups for multiple sections? The patch I have posted doesn't do
any packing. Or do you mean that using a double array can break hotplog?
Not that this would change anything, alloc_pages_exact is really a
better solution, I am just curious ;) 

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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