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: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -67,12 +67,6 @@ struct btrfs_ref;
 
 #define BTRFS_OLDEST_GENERATION	0ULL
 
-/*
- * the max metadata block size.  This limit is somewhat artificial,
- * but the memmove costs go through the roof for larger blocks.
- */
-#define BTRFS_MAX_METADATA_BLOCKSIZE 65536
-
 /*
  * we can actually store much bigger names, but lets not confuse the rest
  * of linux

fs/btrfs/extent_io.c

@@ -5053,12 +5053,7 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
 	atomic_set(&eb->refs, 1);
 	atomic_set(&eb->io_pages, 0);
 
-	/*
-	 * Sanity checks, currently the maximum is 64k covered by 16x 4k pages
-	 */
-	BUILD_BUG_ON(BTRFS_MAX_METADATA_BLOCKSIZE
-		> MAX_INLINE_EXTENT_BUFFER_SIZE);
-	BUG_ON(len > MAX_INLINE_EXTENT_BUFFER_SIZE);
+	ASSERT(len <= BTRFS_MAX_METADATA_BLOCKSIZE);
 
 	return eb;
 }

fs/btrfs/extent_io.h

@@ -6,6 +6,7 @@
 #include <linux/rbtree.h>
 #include <linux/refcount.h>
 #include <linux/fiemap.h>
+#include <linux/btrfs_tree.h>
 #include "ulist.h"
 
 /*
@@ -74,8 +75,7 @@ typedef blk_status_t (submit_bio_hook_t)(struct inode *inode, struct bio *bio,
 typedef blk_status_t (extent_submit_bio_start_t)(struct inode *inode,
 		struct bio *bio, u64 dio_file_offset);
 
-#define INLINE_EXTENT_BUFFER_PAGES 16
-#define MAX_INLINE_EXTENT_BUFFER_SIZE (INLINE_EXTENT_BUFFER_PAGES * PAGE_SIZE)
+#define INLINE_EXTENT_BUFFER_PAGES     (BTRFS_MAX_METADATA_BLOCKSIZE / PAGE_SIZE)
 struct extent_buffer {
 	u64 start;
 	unsigned long len;

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