Re: [RFC PATCH] page_cgroup: Reduce allocation overhead forpage_cgroup array for CONFIG_SPARSEMEM

From: Michal Hocko
Date: Thu Feb 24 2011 - 04:35:28 EST

On Thu 24-02-11 08:52:27, KAMEZAWA Hiroyuki wrote:
> On Wed, 23 Feb 2011 10:19:22 -0800
> Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> 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
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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