> Stop right here. Instead of improving existing swap api, you just
Hi Pavel!
The existing swap API as it stands is inadequate for an efficient
synchronous interface (e.g. for swapping to RAM). Both Nitin
and I independently have found this to be true. But swap-to-RAM
is very useful in some cases (swap-to-kernel-compressed-RAM
and swap-to-hypervisor-RAM and maybe others) that were not even
conceived many years ago at the time the existing swap API was
designed for swap-to-disk. Swap-to-RAM can relieve memory
pressure faster and more resource-efficient than swap-to-device
but must assume that RAM available for swap-to-RAM is dynamic
(not fixed in size). (And swap-to-SSD, when the SSD is an
I/O device on an I/O bus is NOT the same as swap-to-RAM.)
In my opinion, frontswap is NOT a new API, but the simplest
possible extension of the existing swap API to allow for
efficient swap-to-RAM. Avi's comments about a new API
(as he explained later in the thread) refer to a new API
between kernel and hypervisor, what is essentially the
Transcendent Memory interface. Frontswap was separated from
the tmem dependency to enable Nitin's swap-to-kernel-compressed-RAM
and the possibility that there may be other interesting
swap-to-RAM uses.
Does this help?
Dan
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