From: Josef Bacik <josef@toxicpanda.com>
Date: Fri, 11 Jan 2019 10:21:02 -0500
Subject: btrfs: wakeup cleaner thread when adding delayed iput
Git-commit: fd340d0f68cc87badfc9efcb226f23a5428826a0
Patch-mainline: v5.0-rc3
References: bsc#1165949

The cleaner thread usually takes care of delayed iputs, with the
exception of the btrfs_end_transaction_throttle path.  Delaying iputs
means we are potentially delaying the eviction of an inode and it's
respective space.  The cleaner thread only gets woken up every 30
seconds, or when we require space.  If there are a lot of inodes that
need to be deleted we could induce a serious amount of latency while we
wait for these inodes to be evicted.  So instead wakeup the cleaner if
it's not already awake to process any new delayed iputs we add to the
list.  If we suddenly need space we will less likely be backed up
behind a bunch of inodes that are waiting to be deleted, and we could
possibly free space before we need to get into the flushing logic which
will save us some latency.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Acked-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/ctree.h   |    4 ++++
 fs/btrfs/disk-io.c |    3 +++
 fs/btrfs/inode.c   |    2 ++
 3 files changed, 9 insertions(+)

--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -756,6 +756,10 @@ struct btrfs_delayed_root;
  */
 #define BTRFS_FS_BALANCE_RUNNING		18
 
+
+/* Indicate that the cleaner thread is awake and doing something. */
+#define BTRFS_FS_CLEANER_RUNNING		19
+
 struct btrfs_fs_info {
 	u8 fsid[BTRFS_FSID_SIZE];
 	u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1754,6 +1754,8 @@ static int cleaner_kthread(void *arg)
 	while (1) {
 		again = 0;
 
+		set_bit(BTRFS_FS_CLEANER_RUNNING, &fs_info->flags);
+
 		/* Make the cleaner go to sleep early. */
 		if (btrfs_need_cleaner_sleep(fs_info))
 			goto sleep;
@@ -1800,6 +1802,7 @@ static int cleaner_kthread(void *arg)
 		 */
 		btrfs_delete_unused_bgs(fs_info);
 sleep:
+		clear_bit(BTRFS_FS_CLEANER_RUNNING, &fs_info->flags);
 		if (kthread_should_park())
 			kthread_parkme();
 		if (kthread_should_stop())
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3276,6 +3276,8 @@ void btrfs_run_delayed_iputs(struct btrf
 		spin_lock(&fs_info->delayed_iput_lock);
 	}
 	spin_unlock(&fs_info->delayed_iput_lock);
+	if (!test_bit(BTRFS_FS_CLEANER_RUNNING, &fs_info->flags))
+		wake_up_process(fs_info->cleaner_kthread);
 }
 
 /*