linux-kernel - Re: [PATCH v2] mm: Enable suspend-only swap spaces

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Message-ID: <YO6Zk5wwpdqwwGUs@dhcp22.suse.cz>
Date:   Wed, 14 Jul 2021 10:00:19 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Evan Green <evgreen@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pavel Machek <pavel@....cz>, Alex Shi <alexs@...nel.org>,
        Alistair Popple <apopple@...dia.com>,
        Jens Axboe <axboe@...nel.dk>,
        Johannes Weiner <hannes@...xchg.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Minchan Kim <minchan@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v2] mm: Enable suspend-only swap spaces

On Wed 14-07-21 09:51:13, David Hildenbrand wrote:
[...]
> Anyhow, the proposal here does not sound completely crazy to me, although
> it's unfortunate how we decided to mangle hibernation and swapping into the
> same mechanism originally; a different interface to active "hibernation only
> backends" would be cleaner than doing a "swapon ..." without swapping.

Completely agreed! And I suspect that a special swap flag just digs that
hole even deeper. While the flag might look simple enough now I am a bit
worried this will open traps in the future.

I am not saying the idea is crazy either, it is just a hack on top of
the existing hack and as such it requires a very good reasoning. So far
I have heard rather vague justification and I am especially curious
about the "no mixing with the regular swapout" concern. It might be very
well the case that there are more usecases which would benefit from it.
-- 
Michal Hocko
SUSE Labs