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Date: Tue, 9 Sep 2008 14:12:44 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Nick Piggin <nickpiggin@...oo.com.au>
Cc: balbir@...ux.vnet.ibm.com,
Andrew Morton <akpm@...ux-foundation.org>, hugh@...itas.com,
menage@...gle.com, xemul@...nvz.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [RFC][PATCH] Remove cgroup member from struct page
On Tue, 9 Sep 2008 15:00:10 +1000
Nick Piggin <nickpiggin@...oo.com.au> wrote:
> > maybe a routine like SPARSEMEM is a choice.
> >
> > Following is pointer pre-allocation. (just pointer, not page_cgroup itself)
> > ==
> > #define PCG_SECTION_SHIFT (10)
> > #define PCG_SECTION_SIZE (1 << PCG_SECTION_SHIFT)
> >
> > struct pcg_section {
> > struct page_cgroup **map[PCG_SECTION_SHIFT]; //array of pointer.
> > };
> >
> > struct page_cgroup *get_page_cgroup(unsigned long pfn)
> > {
> > struct pcg_section *sec;
> > sec = pcg_section[(pfn >> PCG_SECTION_SHIFT)];
> > return *sec->page_cgroup[(pfn & ((1 << PCG_SECTTION_SHIFT) - 1];
> > }
> > ==
> > If we go extreme, we can use kmap_atomic() for pointer array.
> >
> > Overhead of pointer-walk is not so bad, maybe.
> >
> > For 64bit systems, we can find a way like SPARSEMEM_VMEMMAP.
>
> Yes I too think that would be the ideal way to go to get the best of
> performance in the enabled case. However Balbir I believe is interested
> in memory savings if not all pages have cgroups... I don't know, I don't
> care so much about the "enabled" case, so I'll leave you two to fight it
> out :)
>
I'll add a new patch on my set.
Balbir, are you ok to CONFIG_CGROUP_MEM_RES_CTLR depends on CONFIG_SPARSEMEM ?
I thinks SPARSEMEM(SPARSEMEM_VMEMMAP) is widely used in various archs now.
Thanks,
-Kame
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