btrfs: track DIO bytes in flight

When diagnosing a slowdown of generic/224 I noticed we were not doing
anything when calling into shrink_delalloc().  This is because all
writes in 224 are O_DIRECT, not delalloc, and thus our delalloc_bytes
counter is 0, which short circuits most of the work inside of
shrink_delalloc().  However O_DIRECT writes still consume metadata
resources and generate ordered extents, which we can still wait on.

Fix this by tracking outstanding DIO write bytes, and use this as well
as the delalloc bytes counter to decide if we need to lookup and wait on
any ordered extents.  If we have more DIO writes than delalloc bytes
we'll go ahead and wait on any ordered extents regardless of our flush
state as flushing delalloc is likely to not gain us anything.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
[ use dio instead of odirect in identifiers ]
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index f6bb6039fa4c..52889da69113 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -195,8 +195,11 @@ static int __btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
 	if (type != BTRFS_ORDERED_IO_DONE && type != BTRFS_ORDERED_COMPLETE)
 		set_bit(type, &entry->flags);
 
-	if (dio)
+	if (dio) {
+		percpu_counter_add_batch(&fs_info->dio_bytes, len,
+					 fs_info->delalloc_batch);
 		set_bit(BTRFS_ORDERED_DIRECT, &entry->flags);
+	}
 
 	/* one ref for the tree */
 	refcount_set(&entry->refs, 1);
@@ -468,6 +471,10 @@ void btrfs_remove_ordered_extent(struct inode *inode,
 	if (root != fs_info->tree_root)
 		btrfs_delalloc_release_metadata(btrfs_inode, entry->len, false);
 
+	if (test_bit(BTRFS_ORDERED_DIRECT, &entry->flags))
+		percpu_counter_add_batch(&fs_info->dio_bytes, -entry->len,
+					 fs_info->delalloc_batch);
+
 	tree = &btrfs_inode->ordered_tree;
 	spin_lock_irq(&tree->lock);
 	node = &entry->rb_node;