From: Josef Bacik <josef@toxicpanda.com>
Date: Tue, 21 Jul 2020 10:22:24 -0400
Subject: btrfs: add the data transaction commit logic into
 may_commit_transaction
Git-commit: a1ed0a8216f7c7305ccfaa2c93b498f10b340ede
Patch-mainline: v5.10-rc1
References: bsc#1135481

Data space flushing currently unconditionally commits the transaction
twice in a row, and the last time it checks if there's enough pinned
extents to satisfy its reservation before deciding to commit the
transaction for the 3rd and final time.

Encode this logic into may_commit_transaction().  In the next patch we
will pass in U64_MAX for bytes_needed the first two times, and the final
time we will pass in the actual bytes we need so the normal logic will
apply.

This patch exists solely to make the logical changes I will make to the
flushing state machine separate to make it easier to bisect any
performance related regressions.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Tested-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.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/space-info.c |   31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -456,21 +456,33 @@ static void shrink_delalloc(struct btrfs
  * will return -ENOSPC.
  */
 static int may_commit_transaction(struct btrfs_fs_info *fs_info,
-				  struct btrfs_space_info *space_info)
+				  struct btrfs_space_info *space_info,
+				  u64 bytes_needed)
 {
 	struct reserve_ticket *ticket = NULL;
 	struct btrfs_block_rsv *delayed_rsv = &fs_info->delayed_block_rsv;
 	struct btrfs_block_rsv *delayed_refs_rsv = &fs_info->delayed_refs_rsv;
 	struct btrfs_block_rsv *trans_rsv = &fs_info->trans_block_rsv;
 	struct btrfs_trans_handle *trans;
-	u64 bytes_needed;
 	u64 reclaim_bytes = 0;
 	u64 cur_free_bytes = 0;
+	bool do_commit = false;
 
 	trans = (struct btrfs_trans_handle *)current->journal_info;
 	if (trans)
 		return -EAGAIN;
 
+	/*
+	 * If we are data and have passed in U64_MAX we just want to
+	 * unconditionally commit the transaction to match the previous data
+	 * flushing behavior.
+	 */
+	if ((space_info->flags & BTRFS_BLOCK_GROUP_DATA) &&
+	    bytes_needed == U64_MAX) {
+		do_commit = true;
+		goto check_pinned;
+	}
+
 	spin_lock(&space_info->lock);
 	cur_free_bytes = btrfs_space_info_used(space_info, true);
 	if (cur_free_bytes < space_info->total_bytes)
@@ -484,7 +496,8 @@ static int may_commit_transaction(struct
 	else if (!list_empty(&space_info->tickets))
 		ticket = list_first_entry(&space_info->tickets,
 					  struct reserve_ticket, list);
-	bytes_needed = (ticket) ? ticket->bytes : 0;
+	if (ticket)
+		bytes_needed = ticket->bytes;
 
 	if (bytes_needed > cur_free_bytes)
 		bytes_needed -= cur_free_bytes;
@@ -494,6 +507,7 @@ static int may_commit_transaction(struct
 
 	if (!bytes_needed)
 		return 0;
+check_pinned:
 	trans = btrfs_join_transaction(fs_info->extent_root);
 	if (IS_ERR(trans))
 		return PTR_ERR(trans);
@@ -503,15 +517,18 @@ static int may_commit_transaction(struct
 	 * we have block groups that are going to be freed, allowing us to
 	 * possibly do a chunk allocation the next loop through.
 	 */
-	if (test_bit(BTRFS_TRANS_HAVE_FREE_BGS, &trans->transaction->flags) ||
+	if (do_commit ||
+	    test_bit(BTRFS_TRANS_HAVE_FREE_BGS, &trans->transaction->flags) ||
 	    __percpu_counter_compare(&space_info->total_bytes_pinned,
 				   bytes_needed,
 				   BTRFS_TOTAL_BYTES_PINNED_BATCH) >= 0)
 		goto commit;
 
 	/*
-	 * See if there is some space in the delayed insertion reservation for
-	 * this reservation.
+	 * See if there is some space in the delayed insertion reserve for this
+	 * reservation.  If the space_info's don't match (like for DATA or
+	 * SYSTEM) then just go enospc, reclaiming this space won't recover any
+	 * space to satisfy those reservations.
 	 */
 	if (space_info != delayed_rsv->space_info)
 		goto enospc;
@@ -615,7 +632,7 @@ static int flush_space(struct btrfs_fs_i
 		btrfs_wait_on_delayed_iputs(fs_info);
 		break;
 	case COMMIT_TRANS:
-		ret = may_commit_transaction(fs_info, space_info);
+		ret = may_commit_transaction(fs_info, space_info, num_bytes);
 		break;
 	default:
 		ret = -ENOSPC;