Unverified Commit 66c14dcc authored by Jan Kara's avatar Jan Kara Committed by Christian Brauner
Browse files

writeback: Avoid softlockup when switching many inodes 



process_inode_switch_wbs_work() can be switching over 100 inodes to a
different cgroup. Since switching an inode requires counting all dirty &
under-writeback pages in the address space of each inode, this can take
a significant amount of time. Add a possibility to reschedule after
processing each inode to avoid softlockups.

Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent e1b849cf

fs/fs-writeback.c

+10 −1
Original line number Diff line number Diff line
@@ -500,6 +500,7 @@ static void process_inode_switch_wbs(struct bdi_writeback *new_wb, 
	 */

	down_read(&bdi->wb_switch_rwsem);



	inodep = isw->inodes;

	/*

	 * By the time control reaches here, RCU grace period has passed

	 * since I_WB_SWITCH assertion and all wb stat update transactions
@@ -510,6 +511,7 @@ static void process_inode_switch_wbs(struct bdi_writeback *new_wb, 
	 * gives us exclusion against all wb related operations on @inode

	 * including IO list manipulations and stat updates.

	 */

relock:

	if (old_wb < new_wb) {

		spin_lock(&old_wb->list_lock);

		spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
@@ -518,10 +520,17 @@ static void process_inode_switch_wbs(struct bdi_writeback *new_wb, 
		spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);

	}



	for (inodep = isw->inodes; *inodep; inodep++) {

	while (*inodep) {

		WARN_ON_ONCE((*inodep)->i_wb != old_wb);

		if (inode_do_switch_wbs(*inodep, old_wb, new_wb))

			nr_switched++;

		inodep++;

		if (*inodep && need_resched()) {

			spin_unlock(&new_wb->list_lock);

			spin_unlock(&old_wb->list_lock);

			cond_resched();

			goto relock;

		}

	}



	spin_unlock(&new_wb->list_lock);