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

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Date:   Mon, 10 Jun 2019 23:36:55 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Yang Shi <yang.shi@...ux.alibaba.com>, ying.huang@...el.com,
        hannes@...xchg.org, mhocko@...e.com, mgorman@...hsingularity.net,
        kirill.shutemov@...ux.intel.com, josef@...icpanda.com,
        hughd@...gle.com, shakeelb@...gle.com, hdanton@...a.com,
        akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v7 PATCH 1/2] mm: vmscan: remove double slab pressure by
 inc'ing sc->nr_scanned

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
SUSE L3