btrfs: calculate inline extent buffer page size based on page size

Btrfs only support 64K as maximum node size, thus for 4K page system, we
would have at most 16 pages for one extent buffer.

For a system using 64K page size, we would really have just one page.

While we always use 16 pages for extent_buffer::pages, this means for
systems using 64K pages, we are wasting memory for 15 page pointers
which will never be used.

Calculate the array size based on page size and the node size maximum.

- for systems using 4K page size, it will stay 16 pages
- for systems using 64K page size, it will be 1 page

Move the definition of BTRFS_MAX_METADATA_BLOCKSIZE to btrfs_tree.h, to
avoid circular inclusion of ctree.h.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
index 6b885982ece6..58d7cff9afb1 100644
--- a/include/uapi/linux/btrfs_tree.h
+++ b/include/uapi/linux/btrfs_tree.h
@@ -299,7 +299,8 @@
  */
 #define BTRFS_STRING_ITEM_KEY	253
 
-
+/* Maximum metadata block size (nodesize) */
+#define BTRFS_MAX_METADATA_BLOCKSIZE			65536
 
 /* 32 bytes in various csum fields */
 #define BTRFS_CSUM_SIZE 32