On Sun, Sep 12, 2010 at 11:49:46PM +0800, Wu Fengguang wrote:
> The dirty_ratio was siliently limited in global_dirty_limits() to >= 5%.
> This is not a user expected behavior. And it's inconsistent with
> calc_period_shift(), which uses the plain vm_dirty_ratio value.
>
> Let's rip the arbitrary internal bound. It may impact some very weird
> user space applications. However we are going to dynamicly sizing the
> dirty limits anyway, which may well break such applications, too.
>
> At the same time, fix balance_dirty_pages() to work with the
> dirty_thresh=0 case. This allows applications to proceed when
> dirty+writeback pages are all cleaned.
>
> And ">" fits with the name "exceeded" better than ">=" does. Neil
> think it is an aesthetic improvement as well as a functional one :)
>
> CC: Jan Kara <jack@xxxxxxx>
> Proposed-by: Con Kolivas <kernel@xxxxxxxxxxx>
> Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
> Reviewed-by: Neil Brown <neilb@xxxxxxx>
> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> ---
> fs/fs-writeback.c | 2 +-
> mm/page-writeback.c | 16 +++++-----------
> 2 files changed, 6 insertions(+), 12 deletions(-)
>
> --- linux-next.orig/mm/page-writeback.c 2010-08-29 08:10:30.000000000 +0800
> +++ linux-next/mm/page-writeback.c 2010-08-29 08:12:08.000000000 +0800
> @@ -415,14 +415,8 @@ void global_dirty_limits(unsigned long *
>
> if (vm_dirty_bytes)
> dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
> - else {
> - int dirty_ratio;
> -
> - dirty_ratio = vm_dirty_ratio;
> - if (dirty_ratio < 5)
> - dirty_ratio = 5;
> - dirty = (dirty_ratio * available_memory) / 100;
> - }
> + else
> + dirty = (vm_dirty_ratio * available_memory) / 100;
>
What kernel is this? In a recent mainline kernel and on linux-next, this
is
dirty = (dirty_ratio * available_memory) / 100;
i.e. * instead of +. With +, the value for dirty is almost always going
to be simply 1%.
> if (dirty_background_bytes)
> background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
> @@ -510,7 +504,7 @@ static void balance_dirty_pages(struct a
> * catch-up. This avoids (excessively) small writeouts
> * when the bdi limits are ramping up.
> */
> - if (nr_reclaimable + nr_writeback <
> + if (nr_reclaimable + nr_writeback <=
> (background_thresh + dirty_thresh) / 2)
> break;
>
> @@ -542,8 +536,8 @@ static void balance_dirty_pages(struct a
> * the last resort safeguard.
> */
> dirty_exceeded =
> - (bdi_nr_reclaimable + bdi_nr_writeback >= bdi_thresh)
> - || (nr_reclaimable + nr_writeback >= dirty_thresh);
> + (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh)
> + || (nr_reclaimable + nr_writeback > dirty_thresh);
>
> if (!dirty_exceeded)
> break;
> --- linux-next.orig/fs/fs-writeback.c 2010-08-29 08:12:51.000000000 +0800
> +++ linux-next/fs/fs-writeback.c 2010-08-29 08:12:53.000000000 +0800
> @@ -574,7 +574,7 @@ static inline bool over_bground_thresh(v
> global_dirty_limits(&background_thresh, &dirty_thresh);
>
> return (global_page_state(NR_FILE_DIRTY) +
> - global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
> + global_page_state(NR_UNSTABLE_NFS) > background_thresh);
> }
>
> /*
>
>
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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