linux-kernel - Re: [PATCH v3] mm: Enable suspend-only swap spaces

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Message-Id: <20210721150926.ce56fb8b5fa733d9727bd37e@linux-foundation.org>
Date:   Wed, 21 Jul 2021 15:09:26 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Evan Green <evgreen@...omium.org>
Cc:     linux-api@...r.kernel.org, David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...e.com>, Pavel Machek <pavel@....cz>,
        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 v3] mm: Enable suspend-only swap spaces

On Wed, 21 Jul 2021 14:40:28 -0700 Evan Green <evgreen@...omium.org> wrote:

> Currently it's not possible to enable hibernation without also enabling
> generic swap for a given swap area. These two use cases are not the
> same. For example there may be users who want to enable hibernation,
> but whose drives don't have the write endurance for generic swap
> activities. Swap and hibernate also have different security/integrity
> requirements, prompting folks to possibly set up something like block-level
> integrity for swap and image-level integrity for hibernate. Keeping swap
> and hibernate separate in these cases becomes not just a matter of
> preference, but correctness.
> 
> Add a new SWAP_FLAG_NOSWAP that adds a swap region but refuses to allow
> generic swapping to it. This region can still be wired up for use in
> suspend-to-disk activities, but will never have regular pages swapped to
> it. This flag will be passed in by utilities like swapon(8), usage would
> probably look something like: swapon -o noswap /dev/sda2.

Will patches to swapon and its manpage be prepared?

> Swap regions with SWAP_FLAG_NOSWAP set will not appear in /proc/meminfo
> under SwapTotal and SwapFree, since they are not usable as general swap.
>