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

[Vivek Goyal <vgoyal@redhat.com>]

On Wed, Jul 28, 2010 at 11:44:02AM +0900, KAMEZAWA Hiroyuki wrote:
> On Tue, 27 Jul 2010 22:39:04 -0400
> Vivek Goyal <vgoyal@redhat.com> wrote:
> 
> > 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.
> > 
> yes. you can use css_lookup() even if it's slow.
> 

Ok.

> > 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?
> > 
> blk_cgroup id can be attached whenever you wants. please overwrite 
> page_cgroup->blk_cgroup when it's necessary.

> Did you read Ikeda's patch ? I myself doesn't have patches at this point. 
> This is just for make a room for recording blkio-ID, which was requested
> for a year.

I have not read his patches yet. IIRC, previously there were issues
regarding which group should be charged for the page. The person who
allocated it or the thread which did last write to it etc... I guess
we can sort that out later.

> 
> Hmm, but page-allocation-time doesn't sound very good for me.
> 

Why?

Vivek

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