Re: [Libguestfs] [PATCH nbdkit] file: Implement cache=none and fadvise=normal|random|sequential.
On Fri, Aug 07, 2020 at 05:29:24PM +0300, Nir Soffer wrote:
On Fri, Aug 7, 2020 at 5:07 PM Richard W.M. Jones
<rjones(a)redhat.com> wrote:
> These ones?
> https://www.redhat.com/archives/libguestfs/2020-August/msg00078.html
No, we had a bug when copying image from glance caused sanlock timeouts
because of the unpredictable page cache flushes.
We tried to use fadvice but it did not help. The only way to avoid such issues
is with O_SYNC or O_DIRECT. O_SYNC is much slower but this is the path
we took for now in this flow.
I'm interested in more background about this, because while it is true
that O_DIRECT and POSIX_FADV_DONTNEED are not exactly equivalent, I
think I've shown here that DONTNEED can be used to avoid polluting the
page cache.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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