writeback: remove the internal 5% low bound on dirty_ratio (4cbec4c8) · Commits · 戴 / test

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>

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;

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