btrfs: allow extent buffer helpers to skip cross-page handling

Currently btrfs extent buffer helpers are doing all the cross-page
handling, as there is no guarantee that all those eb pages are
contiguous.

However on systems with enough memory, there is a very high chance the
page cache for btree_inode are allocated with physically contiguous
pages.

In that case, we can skip all the complex cross-page handling, thus
speeding up the code.

This patch adds a new member, extent_buffer::addr, which is only set to
non-NULL if all the extent buffer pages are physically contiguous.

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, 7 insertions, 0 deletions

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 021040b3117e..c2c6bfba63c0 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -78,6 +78,13 @@ struct extent_buffer {
 	unsigned long len;
 	unsigned long bflags;
 	struct btrfs_fs_info *fs_info;
+
+	/*
+	 * The address where the eb can be accessed without any cross-page handling.
+	 * This can be NULL if not possible.
+	 */
+	void *addr;
+
 	spinlock_t refs_lock;
 	atomic_t refs;
 	int read_mirror;