Messages in this thread | | | Date | Thu, 2 Oct 2008 17:06:46 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority |
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On Fri, 3 Oct 2008 09:58:49 +1000 Dave Chinner <david@fromorbit.com> wrote:
> 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...
Yup. There are plenty of spare bits in buffer_head.b_state. set_buffer_kludge()?
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