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SubjectRe: [PATCHSET v3.1 0/7] data integrity: Stabilize pages during writeback for various fses
On Wed 11-05-11 01:12:13, OGAWA Hirofumi wrote:
> Jan Kara <jack@suse.cz> writes:
>
> >> Did you already consider, to copy only if page was writeback (like
> >> copy-on-write)? I.e. if page is on I/O, copy, then switch the page for
> >> writing new data.
> > Yes, that was considered as well. We'd have to essentially migrate the
> > page that is under writeback and should be written to. You are going to pay
> > the cost of page allocation, copy, increased memory & cache pressure.
> > Depending on your backing storage and workload this may or may not be better
> > than waiting for IO...
>
> Maybe possible, but you really think on usual case just blocking is
> better?
Define usual case... As Christoph noted, we don't currently have a real
practical case where blocking would matter (since frequent rewrites are
rather rare). So defining what is usual when we don't have a single real
case is kind of tough ;)

Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR


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