Re: [RFC][PATCH 0/3] page cgroup diet

[Konstantin Khlebnikov <khlebnikov-GEFAQzZX7r8dnm+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.