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Date:   Wed, 21 Jul 2021 15:09:26 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Evan Green <evgreen@chromium.org>
Cc:     linux-api@vger.kernel.org, David Hildenbrand <david@redhat.com>,
        Michal Hocko <mhocko@suse.com>, Pavel Machek <pavel@ucw.cz>,
        Alex Shi <alexs@kernel.org>,
        Alistair Popple <apopple@nvidia.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Minchan Kim <minchan@kernel.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Vlastimil Babka <vbabka@suse.cz>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH v3] mm: Enable suspend-only swap spaces
Message-Id: <20210721150926.ce56fb8b5fa733d9727bd37e@linux-foundation.org>
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On Wed, 21 Jul 2021 14:40:28 -0700 Evan Green <evgreen@chromium.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.
>