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

On Wed, 21 Jul 2021 14:40:28 -0700 Evan Green [off-list ref] 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.