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SubjectRe: Linux 2.6.29
On Wed, 25 Mar 2009, Jens Axboe wrote:
> On Wed, Mar 25 2009, Ric Wheeler wrote:
> > Jens Axboe wrote:
> >>
> >> Another problem is that FLUSH_CACHE sucks. Really. And not just on
> >> ext3/ordered, generally. Write a 50 byte file, fsync, flush cache and
> >> wit for the world to finish. Pretty hard to teach people to use a nicer
> >> fdatasync(), when the majority of the cost now becomes flushing the
> >> cache of that 1TB drive you happen to have 8 partitions on. Good luck
> >> with that.
> >>
> > And, as I am sure that you do know, to add insult to injury, FLUSH_CACHE
> > is per device (not file system).
> >
> > When you issue an fsync() on a disk with multiple partitions, you will
> > flush the data for all of its partitions from the write cache....
>
> Exactly, that's what my (vague) 8 partition reference was for :-)
> A range flush would be so much more palatable.

Tangential question, but am I right in thinking that BIO_RW_BARRIER
similarly bars across all partitions, whereas its WRITE_BARRIER and
DISCARD_BARRIER users would actually prefer it to apply to just one?

Hugh


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