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Commit 47df3dde authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
Browse files

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: default avatarJan Kara <jack@suse.cz>
Reported-by: default avatarPaul Taysom <taysom@chromium.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7cb2ef56

fs/fs-writeback.c

+2 −4
Original line number Original line 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;

	struct backing_dev_info *bdi;





	if (!nr_pages) {

	if (!nr_pages)

		nr_pages = global_page_state(NR_FILE_DIRTY) +

		nr_pages = get_nr_dirty_pages();

				global_page_state(NR_UNSTABLE_NFS);

	}





	rcu_read_lock();

	rcu_read_lock();

	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {

	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {