[PATCH 7/8] btrfs: fix may_commit_transaction to deal with no partial filling

[Josef Bacik <josef@toxicpanda.com>]

Now that we aren't partially filling tickets we may have some slack
space left in the space_info.  We need to account for this in
may_commit_transaction, otherwise we may choose to not commit the
transaction despite it actually having enough space to satisfy our
ticket.

Calculate the free space we have in the space_info, if any.  Then check
to see if its >= the amount of bytes_needed after we've accounted for
the space being used by the delayed refs rsv.  If it's not subtract it
from the bytes_needed before doing the final pinned check.  If we still
don't have enough space then we are truly out of space.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/space-info.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index bd485be783b8..f79afdc04925 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -471,12 +471,19 @@ static int may_commit_transaction(struct btrfs_fs_info *fs_info,
 	struct btrfs_trans_handle *trans;
 	u64 bytes_needed;
 	u64 reclaim_bytes = 0;
+	u64 cur_free_bytes = 0;
 
 	trans = (struct btrfs_trans_handle *)current->journal_info;
 	if (trans)
 		return -EAGAIN;
 
 	spin_lock(&space_info->lock);
+	cur_free_bytes = btrfs_space_info_used(space_info, true);
+	if (cur_free_bytes < space_info->total_bytes)
+		cur_free_bytes = space_info->total_bytes - cur_free_bytes;
+	else
+		cur_free_bytes = 0;
+
 	if (!list_empty(&space_info->priority_tickets))
 		ticket = list_first_entry(&space_info->priority_tickets,
 					  struct reserve_ticket, list);
@@ -522,6 +529,18 @@ static int may_commit_transaction(struct btrfs_fs_info *fs_info,
 		goto commit;
 	bytes_needed -= reclaim_bytes;
 
+	/*
+	 * We don't partially fill tickets anymore, so we could have some free
+	 * bytes in the space_info already, just not enough to satisfy the
+	 * ticket.  If bytes_needed is already below cur_free_bytes after taking
+	 * away the delayed refs and delayed rsv's then we can commit.
+	 * Otherwise subtract our cur_free_bytes from bytes_needed before we
+	 * check pinned.
+	 */
+	if (bytes_needed <= cur_free_bytes)
+		goto commit;
+	bytes_needed -= cur_free_bytes;
+
 	if (__percpu_counter_compare(&space_info->total_bytes_pinned,
 				   bytes_needed,
 				   BTRFS_TOTAL_BYTES_PINNED_BATCH) < 0)
-- 
2.21.0