On 21.07.21 23:40, Evan Green 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.
Just a minor comment, I'd call it rather SWAP_FLAG_HIBERNATE_ONLY and SWAP_FLAG_HIBERNATE_ONLY -- that calls the child by its name.
I think some other flags might not apply with that new flag set, right? For example, does SWAP_FLAG_DISCARD_ONCE or SWP_AREA_DISCARD still have any meaning with the new flag being set?
We should most probably disallow enabling any flag that doesn't make any sense in combination.
Apart from that, I'd love to see a comment in here why the workaround suggested by Michal isn't feasible -- essentially a summary of what we discussed.
I had a quick glimpse and nothing jumed at me, no mm/swapfile.c expert, though :)
-- Thanks, David / dhildenb
