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Commit 4cbec4c8 authored by Wu Fengguang's avatar Wu Fengguang Committed by Linus Torvalds
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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: default avatarWu Fengguang <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>
Proposed-by: default avatarCon Kolivas <kernel@kolivas.org>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Reviewed-by: default avatarNeil Brown <neilb@suse.de>
Reviewed-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michael Rubin <mrubin@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0e093d99

fs/fs-writeback.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

}



/*

mm/page-writeback.c

+5 −11
Original line number Diff line number Diff line
@@ -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;