On Thu, May 05, 2011 at 10:01:34PM +0800, Jan Kara wrote:
> On Thu 05-05-11 20:27:32, Wu Fengguang wrote:
> > On Thu, May 05, 2011 at 05:24:27AM +0800, Jan Kara wrote:
> > > On Mon 02-05-11 11:17:53, Wu Fengguang wrote:
> > > > This removes writeback_control.wb_start and does more straightforward
> > > > sync livelock prevention by setting .older_than_this to prevent extra
> > > > inodes from being enqueued in the first place.
> > > >
> > > > --- linux-next.orig/fs/fs-writeback.c 2011-05-02 11:17:24.000000000 +0800
> > > > +++ linux-next/fs/fs-writeback.c 2011-05-02 11:17:27.000000000 +0800
> > > > @@ -683,10 +672,12 @@ static long wb_writeback(struct bdi_writ
> > > > * (quickly) tag currently dirty pages
> > > > * (maybe slowly) sync all tagged pages
> > > > */
> > > > - if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_sync)
> > > > + if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_sync) {
> > > > write_chunk = LONG_MAX;
> > > > + oldest_jif = jiffies;
> > > > + wbc.older_than_this = &oldest_jif;
> > > > + }
> > > What are the implications of not doing dirty-time livelock avoidance for
> > > other types of writeback? Is that a mistake? I'd prefer to have in
> > > wb_writeback():
> > > if (wbc.for_kupdate)
> > > oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval * 10);
> > > else
> > > oldest_jif = jiffies;
> > > wbc.older_than_this = &oldest_jif;
> > >
> > > And when you have this, you can make wbc.older_than_this just a plain
> > > number and remove all those checks for wbc.older_than_this == NULL.
> >
> > Good point. Here is the fixed patch. Will you send the patch to change
> > the type when the current patches are settled down?
> OK, I will do that.
Thank you.
> > @@ -686,7 +674,9 @@ static long wb_writeback(struct bdi_writ
> > if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_sync)
> > write_chunk = LONG_MAX;
> >
> > - wbc.wb_start = jiffies; /* livelock avoidance */
> > + oldest_jif = jiffies;
> > + wbc.older_than_this = &oldest_jif;
> > +
> I might be already confused with all the code moving around but won't
> this overwrite the value set for the for_kupdate case?
It's the opposite -- it will be overwritten inside the loop by
for_kupdate, which may run for long time and hence need to update
oldest_jif from time to time.
Thanks,
Fengguang
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