[PATCH 4/8] btrfs: add ALLOC_CHUNK_FORCE to the flushing code

[Josef Bacik <josef@toxicpanda.com>]

With my change to no longer take into account the global reserve for
metadata allocation chunks we have this side-effect for mixed block
group fs'es where we are no longer allocating enough chunks for the
data/metadata requirements.  To deal with this add a ALLOC_CHUNK_FORCE
step to the flushing state machine.  This will only get used if we've
already made a full loop through the flushing machinery and tried
committing the transaction.  If we have then we can try and force a
chunk allocation since we likely need it to make progress.  This
resolves the issues I was seeing with the mixed bg tests in xfstests
with my previous patch.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/ctree.h             |  3 ++-
 fs/btrfs/extent-tree.c       | 18 +++++++++++++++++-
 include/trace/events/btrfs.h |  1 +
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 30da075c042e..7cf6ad021d81 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2750,7 +2750,8 @@ enum btrfs_flush_state {
 	FLUSH_DELALLOC		=	5,
 	FLUSH_DELALLOC_WAIT	=	6,
 	ALLOC_CHUNK		=	7,
-	COMMIT_TRANS		=	8,
+	ALLOC_CHUNK_FORCE	=	8,
+	COMMIT_TRANS		=	9,
 };
 
 int btrfs_alloc_data_chunk_ondemand(struct btrfs_inode *inode, u64 bytes);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 667b992d322d..2d0dd70570ca 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4938,6 +4938,7 @@ static void flush_space(struct btrfs_fs_info *fs_info,
 		btrfs_end_transaction(trans);
 		break;
 	case ALLOC_CHUNK:
+	case ALLOC_CHUNK_FORCE:
 		trans = btrfs_join_transaction(root);
 		if (IS_ERR(trans)) {
 			ret = PTR_ERR(trans);
@@ -4945,7 +4946,9 @@ static void flush_space(struct btrfs_fs_info *fs_info,
 		}
 		ret = do_chunk_alloc(trans,
 				     btrfs_metadata_alloc_profile(fs_info),
-				     CHUNK_ALLOC_NO_FORCE);
+				     (state == ALLOC_CHUNK) ?
+				     CHUNK_ALLOC_NO_FORCE :
+				     CHUNK_ALLOC_FORCE);
 		btrfs_end_transaction(trans);
 		if (ret > 0 || ret == -ENOSPC)
 			ret = 0;
@@ -5081,6 +5084,19 @@ static void btrfs_async_reclaim_metadata_space(struct work_struct *work)
 				commit_cycles--;
 		}
 
+		/*
+		 * We don't want to force a chunk allocation until we've tried
+		 * pretty hard to reclaim space.  Think of the case where we
+		 * free'd up a bunch of space and so have a lot of pinned space
+		 * to reclaim.  We would rather use that than possibly create a
+		 * underutilized metadata chunk.  So if this is our first run
+		 * through the flushing state machine skip ALLOC_CHUNK_FORCE and
+		 * commit the transaction.  If nothing has changed the next go
+		 * around then we can force a chunk allocation.
+		 */
+		if (flush_state == ALLOC_CHUNK_FORCE && !commit_cycles)
+			flush_state++;
+
 		if (flush_state > COMMIT_TRANS) {
 			commit_cycles++;
 			if (commit_cycles > 2) {
diff --git a/include/trace/events/btrfs.h b/include/trace/events/btrfs.h
index 63d1f9d8b8c7..dd0e6f8d6b6e 100644
--- a/include/trace/events/btrfs.h
+++ b/include/trace/events/btrfs.h
@@ -1051,6 +1051,7 @@ TRACE_EVENT(btrfs_trigger_flush,
 		{ FLUSH_DELAYED_REFS_NR,	"FLUSH_DELAYED_REFS_NR"},	\
 		{ FLUSH_DELAYED_REFS,		"FLUSH_ELAYED_REFS"},		\
 		{ ALLOC_CHUNK,			"ALLOC_CHUNK"},			\
+		{ ALLOC_CHUNK_FORCE,		"ALLOC_CHUNK_FORCE"},		\
 		{ COMMIT_TRANS,			"COMMIT_TRANS"})
 
 TRACE_EVENT(btrfs_flush_space,
-- 
2.14.3