From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konstantin Khlebnikov <khlebnikov-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>
Subject: Re: [RFC][PATCH 0/3] page cgroup diet
Date: Mon, 19 Mar 2012 23:59:53 +0400
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To: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
Cc: "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>, "cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>, Hugh Dickins <hughd-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Han Ying <yinghan-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>, "Aneesh Kumar K.V" <aneesh.kumar-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, "suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org" <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, "n-horiguchi-PaJj6Psr51x8UrSeD/g0lQ@public.gmane.org" <n-horiguchi-PaJj6Psr51x8UrSeD/g0lQ@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>

KAMEZAWA Hiroyuki wrote:
> This is just an RFC...test is not enough yet.
> 
> I know it's merge window..this post is just for sharing idea.
> 
> This patch merges pc->flags and pc->mem_cgroup into a word. Then,
> memcg's overhead will be 8bytes per page(4096bytes?).
> 
> Because this patch will affect all memory cgroup developers, I'd like to
> show patches before MM Summit. I think we can agree the direction to
> reduce size of page_cgroup..and finally integrate into 'struct page'
> (and remove cgroup_disable= boot option...)
> 
> Patch 1/3 - introduce pc_to_mem_cgroup and hide pc->mem_cgroup
> Patch 2/3 - remove pc->mem_cgroup
> Patch 3/3 - remove memory barriers.
> 
> I'm now wondering when this change should be merged....
> 

This is cool, but maybe we should skip this temporary step and merge all this stuff into page->flags.
I think we can replace zone-id and node-id in page->flags with cumulative dynamically allocated lruvec-id,
so there will be enough space for hundred cgroups even on 32-bit systems.

After lru_lock splitting page to lruvec translation will be much frequently used than page to zone,
so page->zone and page->node translations can be implemented as page->lruvec->zone and page->lruvec->node.