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

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Message-ID: <d99fbe8f-9c80-d407-e848-0be00e3b8886@linux.alibaba.com>
Date:   Tue, 11 Jun 2019 10:12:25 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Oscar Salvador <osalvador@...e.de>, 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 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
>   be reclaimed the next round.

Yes, exactly.

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