Commit 47df3dde authored Sep 11, 2013 by Jan Kara Committed by Linus Torvalds Sep 11, 2013

writeback: fix occasional slow sync(1)



In case when system contains no dirty pages, wakeup_flusher_threads() will
submit WB_SYNC_NONE writeback for 0 pages so wb_writeback() exits
immediately without doing anything, even though there are dirty inodes in
the system.  Thus sync(1) will write all the dirty inodes from a
WB_SYNC_ALL writeback pass which is slow.

Fix the problem by using get_nr_dirty_pages() in wakeup_flusher_threads()
instead of calculating number of dirty pages manually.  That function also
takes number of dirty inodes into account.

Signed-off-by: Jan Kara <jack@suse.cz>
Reported-by: Paul Taysom <taysom@chromium.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 7cb2ef56

fs/fs-writeback.c

+2 −4

Original line number	Diff line number	Diff line
		@@ -1049,10 +1049,8 @@ void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
		{
		struct backing_dev_info *bdi;

		if (!nr_pages) {
		nr_pages = global_page_state(NR_FILE_DIRTY) +
		global_page_state(NR_UNSTABLE_NFS);
		}
		if (!nr_pages)
		nr_pages = get_nr_dirty_pages();

		rcu_read_lock();
		list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {

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