[PATCH 3/4] btrfs: don't miss discards after override-schedule

[Pavel Begunkov <asml.silence@gmail.com>]

If btrfs_discard_schedule_work() is called with override=true, it sets
delay anew regardless how much time left until the timer should have
fired. If delays are long (that can happen, for example, with low
kbps_limit), they might be constantly overriden without having a chance
to run the discard work.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/btrfs/ctree.h   |  1 +
 fs/btrfs/discard.c | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index d43a82dcdfc0..ad71c8c769de 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -469,6 +469,7 @@ struct btrfs_discard_ctl {
 	struct btrfs_block_group *block_group;
 	struct list_head discard_list[BTRFS_NR_DISCARD_LISTS];
 	u64 prev_discard;
+	u64 prev_discard_time;
 	atomic_t discardable_extents;
 	atomic64_t discardable_bytes;
 	u64 max_discard_size;
diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index b6c68e5711f0..c9018b9ccf99 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -381,6 +381,15 @@ void btrfs_discard_schedule_work(struct btrfs_discard_ctl *discard_ctl,
 			delay = max(delay, bg_timeout);
 		}
 
+		if (override && discard_ctl->prev_discard) {
+			u64 elapsed = now - discard_ctl->prev_discard_time;
+
+			if (delay > elapsed)
+				delay -= elapsed;
+			else
+				delay = 0;
+		}
+
 		mod_delayed_work(discard_ctl->discard_workers,
 				 &discard_ctl->work, nsecs_to_jiffies(delay));
 	}
@@ -466,6 +475,7 @@ static void btrfs_discard_workfn(struct work_struct *work)
 	}
 
 	discard_ctl->prev_discard = trimmed;
+	discard_ctl->prev_discard_time = ktime_get_ns();
 
 	/* Determine next steps for a block_group */
 	if (block_group->discard_cursor >= btrfs_block_group_end(block_group)) {
@@ -684,6 +694,7 @@ void btrfs_discard_init(struct btrfs_fs_info *fs_info)
 		INIT_LIST_HEAD(&discard_ctl->discard_list[i]);
 
 	discard_ctl->prev_discard = 0;
+	discard_ctl->prev_discard_time = 0;
 	atomic_set(&discard_ctl->discardable_extents, 0);
 	atomic64_set(&discard_ctl->discardable_bytes, 0);
 	discard_ctl->max_discard_size = BTRFS_ASYNC_DISCARD_DEFAULT_MAX_SIZE;
-- 
2.24.0