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

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Message-Id: <20110224190247.bdc2e6f8.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 24 Feb 2011 19:02:47 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Michal Hocko <mhocko@...e.cz>
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 Feb 2011 10:35:19 +0100
Michal Hocko <mhocko@...e.cz> wrote:

> 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 ;) 
> 

Sorry, it seems I failed to read code correctly. 
You just implemented 2 level table..


Thanks,
-Kame


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