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

From: Yang Shi
Date: Tue Jun 11 2019 - 13:22:26 EST

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
has broken up the relationship between sc->nr_scanned and slab
The sc->nr_scanned can't double slab pressure anymore. So, it sounds
sense to still keep sc->nr_scanned inc'ed. Actually, it would
from adding pressure on slab shrink since excessive sc->nr_scanned
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.

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.