Messages in this thread | | | Date | Fri, 3 Oct 2008 09:58:49 +1000 | From | Dave Chinner <> | Subject | Re: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority |
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On Thu, Oct 02, 2008 at 02:37:13PM -0700, Andrew Morton wrote: > On Thu, 2 Oct 2008 21:22:23 +0200 Jens Axboe <jens.axboe@oracle.com> wrote: > > Can we agree on this patch? > > This change will cause _all_ kjournald writeout to have elevated > priority. The majority of that writeout (in data=ordered mode) is file > data, which we didn't intend to change. > > The risk here is that this will *worsen* latency for plain old read(), > because now kjournald writeout will be favoured. > > There is in fact a good argument for _reducing_ kjournald's IO > priority, not increasing it! > > A better approach might be to mark the relevant buffers/bios as needing > higher priority at submit_bh() time (if that's possible). At least > that way we don't accidentally elevate the priority of the bulk data.
You can do that for submit_bio() by calling bio_set_prio() before submision - I did that for elevating only the XFS journal I/O. submit_bh() doesn't have any way of passing a priority through to it right now...
I should resurrect the XFS patches I had an retest them....
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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