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Re: [Xen-devel] Suspending cached pages



> Hi,
> 
> I used the demo CD to test suspending a domain to disk, hoping to
> migrate suspended domains between Xen machines.  The domain reported
> 62940 kB total memory in /proc/meminfo, with 29800 cached.  This happily
> suspended to a 22965k gzip file, which expands to 65610k when
> decompressed.
> 
> Am I right in thinking that the cache pages were be included, and if so
> are there any thoughts on removing them?

You could in principle use the balloon driver to minimise the
state before doing the suspend.

I fear the balloon driver has rotted slightly as we don't use it
much. We have plans to revive and improve it, but don't have the
man power. I'd be happy to explain to someone what needs doing if
we have a volunteer.

> I seem to recall that before swsusp actually starts its suspension of
> memory to disk scripts prepare the machine state and cache pages are not
> written out.  This means that full performance isn't returned
> immediately after resumption, but presumably it's just as fast to
> re-read the cache back from files on disk rather than pages from a
> suspend file, and it minimises machine state.

I would imagine that restoring the buffer cache in one go is
typically faster than taking a whole string of faults, but it
depends on how well the buffer cache is working for the
application.

Best,
Ian


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