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

[Munehiro Ikeda]

Vivek Goyal wrote, on 07/27/2010 11:13 PM:
> 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@xxxxxxxxxx>  wrote:
> >
> > > On Tue, Jul 27, 2010 at 04:56:29PM +0900, KAMEZAWA Hiroyuki wrote:
> > > > From: KAMEZAWA Hiroyuki<kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > > >
> > > > 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@xxxxxxxxxxxxxx>
> > > > ---
> > > >   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.

Absolutely.
iotrack, a part of blkio cgroup for async write patch I posted, charges
the thread (in exact, blkio-cgroup to which the thread belongs) which
dirtied the page first.  Though it should be controversial and we need
to discuss who should be charged, adding pc->blk_cgroup has no problem
because blkio-cgroup can overwrite it any time, as Kame said above.

Beyond that, adding pc->blk_cgroup is a big step for us.  Now I encode
and store ID in pc->flags.  pc->blk_cgroup is more straight and that
is what we have been looking forward.  Thanks Kame!



--
IKEDA, Munehiro
  NEC Corporation of America
    m-ikeda@xxxxxxxxxxxxx

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/