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xen-devel
Re: [Xen-devel] Invalidating buffer cache in dom0
On 28 May 2005, at 19:49, 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.
This isn't a problem for domU virtual blkdevs: our backend driver
doesn't hook into the page cache, so unless the block device it sends
requests to loops back to the page cache then we will not be affected
by stale buffer cache contents.
Jacob has given a domU direct access to a partition as a virtual
blkdev. It has modified it, and the updates did go straight to disc.
But if dom0 tries to read partition contents itself then it sees stale
page cache data (because the backend completely circumvented the page
cache). I'm surprised that O_DIRECT didn't fix the problem -- I suppose
it's being 'too clever' in this case and checking for potentially dirty
pages in the cache before going direct to disc.
-- Keir
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