On Fri, Jul 9, 2021 at 4:33 PM Andrew Morton [off-list ref] wrote:

On Fri, 9 Jul 2021 16:23:18 -0700 Evan Green [off-list ref] wrote:

quoted

On Fri, Jul 9, 2021 at 3:20 PM Andrew Morton [off-list ref] wrote:

quoted

On Fri,  9 Jul 2021 10:50:48 -0700 Evan Green [off-list ref] wrote:

quoted

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.

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.

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.

This patch doesn't appear to set SWAP_FLAG_NOSWAP anywhere.  Perhaps
there's another patch somewhere which changes the hibernation code?  If
so, can we please have both patches in a series?

There's no other patch, in the kernel at least. SWAP_FLAG_* is exposed
to usermode, which would set it when calling swapon(2). Once this
patch is accepted, I'll have to add the option into util-linux [1], so
that I can use it in my init scripts.

Said a different way, this patch isn't about altering how hibernate
behaves, but about giving usermode the freedom to set up hibernate and
swap independently.

OK, can we please get this into the changelog?  And it would be helpful
to describe how this will be invoked via swapon(8).

Sure, I can augment the commit text to include some of this, and what
it would likely look like from the commandline. I'll send a v3 for
that.

And I expect an update to the swapon syscall's manpage will be in order.

Yes! I was originally planning to do that once this was accepted, but
can also spin it up in parallel if requested.
-Evan