Re: [RFC][PATCH 4/7][memcg] memcg use ID in page_cgroup

[Vivek Goyal <vgoyal@redhat.com>]

On Tue, Jul 27, 2010 at 04:56:29PM +0900, KAMEZAWA Hiroyuki wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> Now, addresses of memory cgroup can be calculated by their ID without complex.
> This patch relplaces pc->mem_cgroup from a pointer to a unsigned short.
> On 64bit architecture, this offers us more 6bytes room per page_cgroup.
> Use 2bytes for blkio-cgroup's page tracking. More 4bytes will be used for
> some light-weight concurrent access.
> 
> We may able to move this id onto flags field but ...go step by step.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  include/linux/page_cgroup.h |    3 ++-
>  mm/memcontrol.c             |   40 +++++++++++++++++++++++++---------------
>  mm/page_cgroup.c            |    2 +-
>  3 files changed, 28 insertions(+), 17 deletions(-)
> 
> Index: mmotm-0719/include/linux/page_cgroup.h
> ===================================================================
> --- mmotm-0719.orig/include/linux/page_cgroup.h
> +++ mmotm-0719/include/linux/page_cgroup.h
> @@ -12,7 +12,8 @@
>   */
>  struct page_cgroup {
>  	unsigned long flags;
> -	struct mem_cgroup *mem_cgroup;
> +	unsigned short mem_cgroup;	/* ID of assigned memory cgroup */
> +	unsigned short blk_cgroup;	/* Not Used..but will be. */

So later I shall have to use virtually indexed arrays in blkio controller?
Or you are just using virtually indexed arrays for lookup speed and
I can continue to use css_lookup() and not worry about using virtually
indexed arrays.

So the idea is that when a page is allocated, also store the blk_group
id and once that page is submitted for writeback, we should be able
to associate it to right blkio group?

Vivek