bcachefs: Prep work for variable size btree node buffers

bcachefs btree nodes are big - typically 256k - and btree roots are
pinned in memory. As we're now up to 18 btrees, we now have significant
memory overhead in mostly empty btree roots.

And in the future we're going to start enforcing that certain btree node
boundaries exist, to solve lock contention issues - analagous to XFS's
AGIs.

Thus, we need to start allocating smaller btree node buffers when we
can. This patch changes code that refers to the filesystem constant
c->opts.btree_node_size to refer to the btree node buffer size -
btree_buf_bytes() - where appropriate.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 12 insertions, 7 deletions

diff --git a/fs/bcachefs/btree_cache.h b/fs/bcachefs/btree_cache.h
index 4e1af5882052..6d33885fdbde 100644
--- a/fs/bcachefs/btree_cache.h
+++ b/fs/bcachefs/btree_cache.h
@@ -74,22 +74,27 @@ static inline bool btree_node_hashed(struct btree *b)
 	     _iter = 0;	_iter < (_tbl)->size; _iter++)			\
 		rht_for_each_entry_rcu((_b), (_pos), _tbl, _iter, hash)
 
-static inline size_t btree_bytes(struct bch_fs *c)
+static inline size_t btree_buf_bytes(const struct btree *b)
 {
-	return c->opts.btree_node_size;
+	return 1UL << b->byte_order;
 }
 
-static inline size_t btree_max_u64s(struct bch_fs *c)
+static inline size_t btree_buf_max_u64s(const struct btree *b)
 {
-	return (btree_bytes(c) - sizeof(struct btree_node)) / sizeof(u64);
+	return (btree_buf_bytes(b) - sizeof(struct btree_node)) / sizeof(u64);
 }
 
-static inline size_t btree_pages(struct bch_fs *c)
+static inline size_t btree_max_u64s(const struct bch_fs *c)
 {
-	return btree_bytes(c) / PAGE_SIZE;
+	return (c->opts.btree_node_size - sizeof(struct btree_node)) / sizeof(u64);
 }
 
-static inline unsigned btree_blocks(struct bch_fs *c)
+static inline size_t btree_sectors(const struct bch_fs *c)
+{
+	return c->opts.btree_node_size >> SECTOR_SHIFT;
+}
+
+static inline unsigned btree_blocks(const struct bch_fs *c)
 {
 	return btree_sectors(c) >> c->block_bits;
 }