On Fri, Nov 02, 2007 at 11:15:32AM +0100, Peter Zijlstra wrote:
> On Fri, 2007-11-02 at 10:21 +0800, Fengguang Wu wrote:
>
> > Interestingly, no background_writeout() appears, but only
> > balance_dirty_pages() and wb_kupdate. Obviously wb_kupdate won't
> > block the process.
>
> Yeah, the background threshold is not (yet) scaled. So it can happen
> that the bdi_dirty limit is below the background limit.
>
> I'm curious though as to these stalls, though, I can't seem to think of
> what goes wrong.. esp since most writeback seems to happen from pdflush.
Me confused too. The new debug patch will confirm whether emerge is
waiting in balance_dirty_pages().
> (or I'm totally misreading it - quite a possible as I'm still recovering
> from a serious cold and not all the green stuff has yet figured out its
> proper place wrt brain cells 'n stuff)
Do take care of yourself.
>
> I still have this patch floating around:
I think this patch is OK for 2.6.24 :-)
Reviewed-by: Fengguang Wu <wfg@xxxxxxxxxxxxxxxx>
>
> ---
> Subject: mm: speed up writeback ramp-up on clean systems
>
> We allow violation of bdi limits if there is a lot of room on the
> system. Once we hit half the total limit we start enforcing bdi limits
> and bdi ramp-up should happen. Doing it this way avoids many small
> writeouts on an otherwise idle system and should also speed up the
> ramp-up.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
>
> ---
> mm/page-writeback.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/mm/page-writeback.c
> ===================================================================
> --- linux-2.6.orig/mm/page-writeback.c 2007-09-28 10:08:33.937415368 +0200
> +++ linux-2.6/mm/page-writeback.c 2007-09-28 10:54:26.018247516 +0200
> @@ -355,8 +355,8 @@ get_dirty_limits(long *pbackground, long
> */
> static void balance_dirty_pages(struct address_space *mapping)
> {
> - long bdi_nr_reclaimable;
> - long bdi_nr_writeback;
> + long nr_reclaimable, bdi_nr_reclaimable;
> + long nr_writeback, bdi_nr_writeback;
> long background_thresh;
> long dirty_thresh;
> long bdi_thresh;
> @@ -376,11 +376,26 @@ static void balance_dirty_pages(struct a
>
> get_dirty_limits(&background_thresh, &dirty_thresh,
> &bdi_thresh, bdi);
> +
> + nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
> + global_page_state(NR_UNSTABLE_NFS);
> + nr_writeback = global_page_state(NR_WRITEBACK);
> +
> bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
> bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
> +
> if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
> break;
>
> + /*
> + * Throttle it only when the background writeback cannot
> + * catch-up. This avoids (excessively) small writeouts
> + * when the bdi limits are ramping up.
> + */
> + if (nr_reclaimable + nr_writeback <
> + (background_thresh + dirty_thresh) / 2)
> + break;
> +
> if (!bdi->dirty_exceeded)
> bdi->dirty_exceeded = 1;
>
>
>
-
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