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xen-devel
Re: [Xen-devel] Invalidating buffer cache in dom0
Ian Pratt wrote:
Have you tried using raw devices? See "man raw". I've never used them,
but I'd be interested to know whether this works. There's an argument
that we should be using them by default, particularly for people using
using cluster filesystems -- caching stuff in dom0 could be very bad.
It is my impression that in recent 2.6 kernels raw devices and O_DIRECT
are the same thing. Actually, I was forced to use O_DIRECT inside my
domU for the self-checkpointing, as otherwise the buffer cache would
inflate the working set and create additional downtime. O_DIRECT works
really well, and minus a ton of bugs I can now self-checkpoint to disk
as well as self-migrate via the network.
O_DIRECT works for writes. However, it seems it still tries to be a
little too clever when reading from a blockdev.
This is not a huge prob for me, just an annoyance that I have to reboot
all the time to flush the cache, but I guess that for a Xen system in
general it would be nice to have consistency of block device contents
between domUs and dom0.
thanks,
Jacob
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