linux-kernel - Re: [v4] mm: khugepaged: avoid overriding min_free

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Message-ID: <20200917092805.GA29887@dhcp22.suse.cz>
Date:   Thu, 17 Sep 2020 11:28:05 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Vijay Balakrishna <vijayb@...ux.microsoft.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Song Liu <songliubraving@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Allen Pais <apais@...rosoft.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [v4] mm: khugepaged: avoid overriding min_free_kbytes set by user

On Wed 16-09-20 23:39:39, Vijay Balakrishna wrote:
> set_recommended_min_free_kbytes need to honor min_free_kbytes set by the
> user.  Post start-of-day THP enable or memory hotplug operations can
> lose user specified min_free_kbytes, in particular when it is higher than
> calculated recommended value.

I was about to recommend a more detailed explanation when I have
realized that this patch is not really needed after all. Unless I am
missing something.

init_per_zone_wmark_min ignores the newly calculated min_free_kbytes if
it is lower than user_min_free_kbytes. So calculated min_free_kbytes >=
user_min_free_kbytes.

Except for value clamping when the value is reduced and this likely
needs fixing. But set_recommended_min_free_kbytes should be fine.
-- 
Michal Hocko
SUSE Labs