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SubjectRe: [PATCH] block: forbid to re-enable I/O stat accounting

Please fix your email headers - what I received was

From: Jerome Marchand <jmarchan@redhat.com>
To: unlisted-recipients:;;@imap1.linux-foundation.org (no To-header on input)
Cc: Jens Axboe <axboe@kernel.dk>


On Thu, 19 Mar 2009 11:36:50 +0100 Jerome Marchand <jmarchan@redhat.com> wrote:

> When we stop I/O stat accounting we stop to update the in-flight
> requests counter and we need this counter to be reliable for
> accounting I/O stats. Unfortunately updating in_flight field may
> affect performance. So, until we have a better solution, just forbid
> to re-enable I/O stat accounting after it has been disabled.

hm. Is it really so hard to just quiesce the device until all in-flight
requests have drained? freeze_bdev() might be a suitable starting point?



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