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

From: Oscar Salvador
Date: Mon Jun 10 2019 - 17:41:28 EST

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
be reclaimed the next round.

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

Oscar Salvador