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Commit a5989bdc authored by Jan Kara's avatar Jan Kara Committed by Jens Axboe
Browse files

fs: Fix busyloop in wb_writeback() 



If all inodes are under writeback (e.g. in case when there's only one inode
with dirty pages), wb_writeback() with WB_SYNC_NONE work basically degrades
to busylooping until I_SYNC flags of the inode is cleared. Fix the problem by
waiting on I_SYNC flags of an inode on b_more_io list in case we failed to
write anything.

Tested-by: default avatarWu Fengguang <fengguang.wu@intel.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 7fa07729

fs/fs-writeback.c

+18 −1
Original line number Diff line number Diff line
@@ -706,6 +706,7 @@ static long wb_writeback(struct bdi_writeback *wb, 
	};

	unsigned long oldest_jif;

	long wrote = 0;

	struct inode *inode;



	if (wbc.for_kupdate) {

		wbc.older_than_this = &oldest_jif;
@@ -747,8 +748,24 @@ static long wb_writeback(struct bdi_writeback *wb, 
		 * If we ran out of stuff to write, bail unless more_io got set

		 */

		if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {

			if (wbc.more_io && !wbc.for_kupdate)

			if (wbc.more_io && !wbc.for_kupdate) {

				if (wbc.nr_to_write < MAX_WRITEBACK_PAGES)

					continue;

				/*

				 * Nothing written. Wait for some inode to

				 * become available for writeback. Otherwise

				 * we'll just busyloop.

				 */

				spin_lock(&inode_lock);

				if (!list_empty(&wb->b_more_io))  {

					inode = list_entry(

							wb->b_more_io.prev,

							struct inode, i_list);

					inode_wait_for_writeback(inode);

				}

				spin_unlock(&inode_lock);

				continue;

			}

			break;

		}

	}