linux-kernel - Re: [PATCH v4] mm: Enable suspend-only swap spaces

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Message-ID: <20210730131541.ighhjiazc4agehcy@ws.net.home>
Date:   Fri, 30 Jul 2021 15:15:41 +0200
From:   Karel Zak <kzak@...hat.com>
To:     Evan Green <evgreen@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, Pavel Machek <pavel@....cz>,
        linux-api@...r.kernel.org, David Hildenbrand <david@...hat.com>,
        Alex Shi <alexs@...nel.org>,
        Alistair Popple <apopple@...dia.com>,
        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>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v4] mm: Enable suspend-only swap spaces

On Mon, Jul 26, 2021 at 05:12:46PM -0700, Evan Green wrote:
> Swap regions with SWAP_FLAG_HIBERNATE_ONLY set will not appear in
> /proc/meminfo under SwapTotal and SwapFree, since they are not usable as
> general swap. These regions do still appear in /proc/swaps.

Off-topic, /proc/swaps is in the same situation like /proc/mounts years ago ...

It does not provide all important information like SWAP_FLAG_DISCARD_PAGES
SWAP_FLAG_DISCARD_ONCE and SWAP_FLAG_HIBERNATE_ONLY flags. 

Users will not able to differentiate between regular and hibernate-only
devices in "swapon" or "cat /proc/swaps" output ;-(

It would be nice to have /proc/swapsinfo with extendible "flags" column.

 Karel


-- 
 Karel Zak  <kzak@...hat.com>
 http://karelzak.blogspot.com