Re: [PATCH v4 06/25] memcg: Make it possible to use the stock formore than one page.

[Glauber Costa]

On 06/20/2012 05:28 PM, Michal Hocko wrote:
> On Mon 18-06-12 14:27:59, Glauber Costa wrote:
> > From: Suleiman Souhlal <ssouhlal@xxxxxxxxxxx>
> >
> > Signed-off-by: Suleiman Souhlal <suleiman@xxxxxxxxxx>
> > Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
> > Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> I am not sure the patch is good to merge on its own without the rest.
> One comment bellow.
>
> > ---
> >   mm/memcontrol.c |   18 +++++++++---------
> >   1 file changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index ce15be4..00b9f1e 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -1998,19 +1998,19 @@ static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
> >   static DEFINE_MUTEX(percpu_charge_mutex);
> >
> >   /*
> > - * Try to consume stocked charge on this cpu. If success, one page is consumed
> > - * from local stock and true is returned. If the stock is 0 or charges from a
> > - * cgroup which is not current target, returns false. This stock will be
> > - * refilled.
> > + * Try to consume stocked charge on this cpu. If success, nr_pages pages are
> > + * consumed from local stock and true is returned. If the stock is 0 or
> > + * charges from a cgroup which is not current target, returns false.
> > + * This stock will be refilled.
> >    */
> > -static bool consume_stock(struct mem_cgroup *memcg)
> > +static bool consume_stock(struct mem_cgroup *memcg, int nr_pages)
> >   {
> >   	struct memcg_stock_pcp *stock;
> >   	bool ret = true;
>
> I guess you want:
> 	if (nr_pages > CHARGE_BATCH)
> 		return false;
>
> because you don't want to try to use stock for THP pages.


The code reads:

+       if (memcg == stock->cached && stock->nr_pages >= nr_pages)
+               stock->nr_pages -= nr_pages;

Isn't stock->nr_pages always <= CHARGE_BATCH by definition?
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