On 04/24/2010 04:49 AM, Nitin Gupta wrote:
I see. So why not implement this as an ordinary swap device, with a
higher priority than the disk device? this way we reuse an API and keep
things asynchronous, instead of introducing a special purpose API.
ramzswap is exactly this: an ordinary swap device which stores every page
in (compressed) memory and its enabled as highest priority swap. Currently,
it stores these compressed chunks in guest memory itself but it is not very
difficult to send these chunks out to host/hypervisor using virtio.
However, it suffers from unnecessary block I/O layer overhead and requires
weird hooks in swap code, say to get notification when a swap slot is freed.
Isn't that TRIM?
OTOH frontswap approach gets rid of any such artifacts and overheads.
(ramzswap: http://code.google.com/p/compcache/)
Maybe we should optimize these overheads instead. Swap used to always
be to slow devices, but swap-to-flash has the potential to make swap act
like an extension of RAM.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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