Btrfs: account for crcs in delayed ref processing

As we delete large extents, we end up doing huge amounts of COW in order
to delete the corresponding crcs.  This adds accounting so that we keep
track of that space and flushing of delayed refs so that we don't build
up too much delayed crc work.

This helps limit the delayed work that must be done at commit time and
tries to avoid ENOSPC aborts because the crcs eat all the global
reserves.

Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
index a764e2340d48..5eb0892396d0 100644
--- a/fs/btrfs/delayed-ref.h
+++ b/fs/btrfs/delayed-ref.h
@@ -88,6 +88,14 @@ struct btrfs_delayed_ref_head {
 	struct rb_node href_node;
 
 	struct btrfs_delayed_extent_op *extent_op;
+
+	/*
+	 * This is used to track the final ref_mod from all the refs associated
+	 * with this head ref, this is not adjusted as delayed refs are run,
+	 * this is meant to track if we need to do the csum accounting or not.
+	 */
+	int total_ref_mod;
+
 	/*
 	 * when a new extent is allocated, it is just reserved in memory
 	 * The actual extent isn't inserted into the extent allocation tree
@@ -138,6 +146,8 @@ struct btrfs_delayed_ref_root {
 	/* total number of head nodes ready for processing */
 	unsigned long num_heads_ready;
 
+	u64 pending_csums;
+
 	/*
 	 * set when the tree is flushing before a transaction commit,
 	 * used by the throttling code to decide if new updates need