Re: [PATCH v2] memcg: trim the per-cpu charge stock instead of draining it

On Thu 20-08-26 09:06:29, Shakeel Butt wrote:
> On Thu, Aug 20, 2026 at 09:06:18AM +0200, Michal Hocko wrote:
> > On Wed 19-08-26 18:20:10, Shakeel Butt wrote:
> > > @@ -2254,9 +2264,12 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
> > >  			empty_slot = i;
> > >  		if (memcg == READ_ONCE(stock->cached[i])) {
> > >  			stock_pages = READ_ONCE(stock->nr_pages[i]) + nr_pages;
> > > +			if (stock_pages > MEMCG_STOCK_HIGH) {
> > > +				memcg_uncharge(memcg,
> > > +					       stock_pages - MEMCG_STOCK_LOW);
> > > +				stock_pages = MEMCG_STOCK_LOW;
> > 
> > I would find it easier to read to keep the update in sync with
> > memcg_uncharge, i.e.
> > 				stock_pages = WRITE_ONCE(stock_pages - MEMCG_STOCK_LOW)
> 
> Sorry I am not sure I understand your suggestion. The WRITE_ONCE() is throwing
> me off.

Sorry, brainfarth on my end. I meant to say that stock_pages should be
updated by the uncharged decrement rather than capping it at MEMCG_STOCK_LOW.
So in fact I meant this
				stock_pages = stock_pages - MEMCG_STOCK_LOW;
but then shortcuted it to a nonsense.

> > > +			}
> > >  			WRITE_ONCE(stock->nr_pages[i], stock_pages);
> > > -			if (stock_pages > MEMCG_CHARGE_BATCH)
> > > -				drain_stock(stock, i);
> > >  			success = true;
> > >  			break;
> > >  		}
> > > -- 
> > > 2.53.0-Meta
> > 
> > -- 
> > Michal Hocko
> > SUSE Labs

-- 
Michal Hocko
SUSE Labs