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writeback: remove the internal 5% low bound on dirty_ratio 

The dirty_ratio was silently 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 remove the internal bound.

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 thinks
it is an aesthetic improvement as well as a functional one :)

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>
Proposed-by: Con Kolivas <kernel@kolivas.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michael Rubin <mrubin@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Wu Fengguang 2010-10-26 14:21:45 -07:00 committed by Linus Torvalds
parent 0e093d9976
commit 4cbec4c8b9
2 changed files with 6 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/fs-writeback.c
View File

@ -582,7 +582,7 @@ static inline bool over_bground_thresh(void)
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);
}
/*

16
mm/page-writeback.c
View File

@ -415,14 +415,8 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
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;
if (dirty_background_bytes)
background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
@ -510,7 +504,7 @@ static void balance_dirty_pages(struct address_space *mapping,
* 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 address_space *mapping,
* 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;