[PATCH 01/14] Fix free/alloc reversal of btree block merge condition

[Valerie Aurora]

To achieve the goal of merging two btree blocks when the merged block
would be 80% full, we want to merge two blocks when their _used_ space
is 40% or lower, not when their _free_ space is 40% or lower. Add some
BUG_ON()'s to catch total_free wrapping around to negative, which was
the visible symptom in this case.

Signed-off-by: Valerie Aurora <val at versity.com>
---
 shared/btree.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/shared/btree.c b/shared/btree.c
index a55da6e..39a9b57 100644
--- a/shared/btree.c
+++ b/shared/btree.c
@@ -49,7 +49,7 @@
  * deletion of a few items doesn't bounce a pair of blocks between
  * splitting and merging.
  */
-#define NGNFS_BTREE_MERGE_FREE_THRESH	(NGNFS_BTREE_MAX_FREE * 40 / 100)
+#define NGNFS_BTREE_MERGE_FREE_THRESH	(NGNFS_BTREE_MAX_FREE * (100 - 40) / 100)
 
 /*
  * If an insertion could be performed after compacting free space, but
@@ -248,15 +248,13 @@ static struct ngnfs_btree_item *insert_item(struct ngnfs_txn_block *tblk,
 					    struct ngnfs_btree_block *bt, u16 ind,
 					    struct ngnfs_btree_key *key, void *val, u16 val_size)
 {
-	struct ngnfs_btree_item *item;
-	u16 bytes;
-	u16 off;
+	u16 off = NGNFS_BLOCK_SIZE - le16_to_cpu(bt->tail_free);
+	struct ngnfs_btree_item *item = item_from_off(bt, off);
+	u16 bytes = aligned_item_size(val_size);
 
 	BUG_ON(ind >= NGNFS_BTREE_MAX_ITEMS);
-
-	bytes = aligned_item_size(val_size);
-	off = NGNFS_BLOCK_SIZE - le16_to_cpu(bt->tail_free);
-	item = item_from_off(bt, off);
+	BUG_ON(le16_to_cpu(bt->tail_free) - bytes > NGNFS_BTREE_MAX_FREE);
+	BUG_ON(le16_to_cpu(bt->total_free) - bytes > NGNFS_BTREE_MAX_FREE);
 
 	memmove_item_headers(tblk, bt, ind, 1);
 	ngnfs_tblk_le16_add_cpu(tblk, &bt->tail_free, -bytes);
@@ -295,6 +293,9 @@ static void delete_item(struct ngnfs_txn_block *tblk, struct ngnfs_btree_block *
 	u16 off = le16_to_cpu(bt->ihdrs[ind].off);
 	u16 nr;
 
+	BUG_ON(le16_to_cpu(bt->tail_free) + bytes > NGNFS_BTREE_MAX_FREE);
+	BUG_ON(le16_to_cpu(bt->total_free) + bytes > NGNFS_BTREE_MAX_FREE);
+
 	if (off == NGNFS_BLOCK_SIZE - le16_to_cpu(bt->tail_free) - bytes)
 		ngnfs_tblk_le16_add_cpu(tblk, &bt->tail_free, bytes);
 	ngnfs_tblk_le16_add_cpu(tblk, &bt->total_free, bytes);
-- 
2.48.1