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    SubjectRe: PATCH] fix potential latency issues in JBD's journal code
    On Sun, 6 Jul 2008 00:15:02 -0400
    Theodore Tso <tytso@MIT.EDU> wrote:

    > On Fri, Jul 04, 2008 at 07:29:29PM -0700, Arjan van de Ven wrote:
    > > @@ -165,7 +165,7 @@ static void journal_do_submit_data(struct
    > > buffer_head **wbuf, int bufs) for (i = 0; i < bufs; i++) {
    > > wbuf[i]->b_end_io = end_buffer_write_sync;
    > > /* We use-up our safety reference in submit_bh() */
    > > - submit_bh(WRITE, wbuf[i]);
    > > + submit_bh(WRITE_SYNC, wbuf[i]);
    > > }
    > > }
    >
    > So I started looking at this patch more closely when trying to
    > replicate it for ext4. Don't you want to only use WRITE_SYNC() only
    > for the very last time in the loop? Otherwise you end up unplugging
    > the queue after each bufferhead, which wouldn't be a good thing,
    > right?

    it's debatable. Because this submit-bh() will sometimes block... it
    wouldn't get IO started for that case. I think this is where I'd like
    Jens to say what he thinks the rules are; clearly the elevator needs to
    treat all of these guys as sync, but maybe the plugging should be ..
    flexible.


    --
    If you want to reach me at my work email, use arjan@linux.intel.com
    For development, discussion and tips for power savings,
    visit http://www.lesswatts.org


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