Re: [v7 PATCH 1/2] mm: vmscan: remove double slab pressure by inc'ing sc->nr_scanned

[Yang Shi]

On 6/11/19 10:12 AM, Yang Shi wrote:
> On 6/10/19 2:36 PM, Oscar Salvador wrote:
> > On Tue, 2019-05-28 at 14:44 +0800, Yang Shi wrote:
> > > The commit 9092c71bb724 ("mm: use sc->priority for slab shrink
> > > targets")
> > > has broken up the relationship between sc->nr_scanned and slab
> > > pressure.
> > > The sc->nr_scanned can't double slab pressure anymore. So, it sounds
> > > no
> > > sense to still keep sc->nr_scanned inc'ed. Actually, it would
> > > prevent
> > > from adding pressure on slab shrink since excessive sc->nr_scanned
> > > would
> > > prevent from scan->priority raise.
> > Hi Yang,
> >
> > I might be misunderstanding this, but did you mean "prevent from scan-
> > priority decreasing"?
> > I guess we are talking about balance_pgdat(), and in case
> > kswapd_shrink_node() returns true (it means we have scanned more than
> > we had to reclaim), raise_priority becomes false, and this does not let
> > sc->priority to be decreased, which has the impact that less pages will
> > Â be reclaimed the next round.
>
> Yes, exactly.

BTW, for the scan priority, the smaller number the higher priority. So, 
either "raise" or "decrease" sounds correct. "raise" means the real 
priority, "decrease" means the number itself.

> > Sorry for bugging here, I just wanted to see if I got this right.