On Mon, Mar 14, 2011 at 09:48:21PM +0100, Jan Kara wrote:
> On Wed 09-03-11 19:07:31, Vivek Goyal wrote:
> > > +static void balance_dirty_pages(struct address_space *mapping,
> > > + unsigned long write_chunk)
> > > +{
> > > + struct backing_dev_info *bdi = mapping->backing_dev_info;
> > > + struct balance_waiter bw;
> > > + struct dirty_limit_state st;
> > > + int dirty_exceeded = check_dirty_limits(bdi, &st);
> > > +
> > > + if (dirty_exceeded < DIRTY_MAY_EXCEED_LIMIT ||
> > > + (dirty_exceeded == DIRTY_MAY_EXCEED_LIMIT &&
> > > + !bdi_task_limit_exceeded(&st, current))) {
> > > + if (bdi->dirty_exceeded &&
> > > + dirty_exceeded < DIRTY_MAY_EXCEED_LIMIT)
> > > + bdi->dirty_exceeded = 0;
> > > /*
> > > - * Increase the delay for each loop, up to our previous
> > > - * default of taking a 100ms nap.
> > > + * In laptop mode, we wait until hitting the higher threshold
> > > + * before starting background writeout, and then write out all
> > > + * the way down to the lower threshold. So slow writers cause
> > > + * minimal disk activity.
> > > + *
> > > + * In normal mode, we start background writeout at the lower
> > > + * background_thresh, to keep the amount of dirty memory low.
> > > */
> > > - pause <<= 1;
> > > - if (pause > HZ / 10)
> > > - pause = HZ / 10;
> > > + if (!laptop_mode && dirty_exceeded == DIRTY_EXCEED_BACKGROUND)
> > > + bdi_start_background_writeback(bdi);
> > > + return;
> > > }
> > >
> > > - /* Clear dirty_exceeded flag only when no task can exceed the limit */
> > > - if (!min_dirty_exceeded && bdi->dirty_exceeded)
> > > - bdi->dirty_exceeded = 0;
> > > + if (!bdi->dirty_exceeded)
> > > + bdi->dirty_exceeded = 1;
> >
> > Will it make sense to move out bdi_task_limit_exceeded() check in a
> > separate if condition statement as follows. May be this is little
> > easier to read.
> >
> > if (dirty_exceeded < DIRTY_MAY_EXCEED_LIMIT) {
> > if (bdi->dirty_exceeded)
> > bdi->dirty_exceeded = 0;
> >
> > if (!laptop_mode && dirty_exceeded == DIRTY_EXCEED_BACKGROUND)
> > bdi_start_background_writeback(bdi);
> >
> > return;
> > }
> >
> > if (dirty_exceeded == DIRTY_MAY_EXCEED_LIMIT &&
> > !bdi_task_limit_exceeded(&st, current))
> > return;
> But then we have to start background writeback here as well. Which is
> actually a bug in the original patch as well! So clearly your way is more
> readable :) I'll change it. Thanks.
I was thinking about that starting of bdi writeback here. But I was
assuming that if we are here then we most likely have visited above
loop of < DIRTY_MAY_EXCEED_LIMIT and started background writeback.
Thanks
Vivek
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