btrfs: reduce width for stripe_len from u64 to u32

Currently btrfs uses fixed stripe length (64K), thus u32 is wide enough
for the usage.

Furthermore, even in the future we choose to enlarge stripe length to
larger values, I don't believe we would want stripe as large as 4G or
larger.

So this patch will reduce the width for all in-memory structures and
parameters, this involves:

- RAID56 related function argument lists
  This allows us to do direct division related to stripe_len.
  Although we will use bits shift to replace the division anyway.

- btrfs_io_geometry structure
  This involves one change to simplify the calculation of both @stripe_nr
  and @stripe_offset, using div64_u64_rem().
  And add extra sanity check to make sure @stripe_offset is always small
  enough for u32.

  This saves 8 bytes for the structure.

- map_lookup structure
  This convert @stripe_len to u32, which saves 8 bytes. (saved 4 bytes,
  and removed a 4-bytes hole)

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, 4 insertions, 4 deletions

diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index f3e28f11cfb6..197877e684df 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -23,11 +23,11 @@ struct btrfs_io_geometry {
 	/* offset of logical address in chunk */
 	u64 offset;
 	/* length of single IO stripe */
-	u64 stripe_len;
+	u32 stripe_len;
+	/* offset of address in stripe */
+	u32 stripe_offset;
 	/* number of stripe where address falls */
 	u64 stripe_nr;
-	/* offset of address in stripe */
-	u64 stripe_offset;
 	/* offset of raid56 stripe into the chunk */
 	u64 raid56_stripe_offset;
 };
@@ -430,7 +430,7 @@ struct map_lookup {
 	u64 type;
 	int io_align;
 	int io_width;
-	u64 stripe_len;
+	u32 stripe_len;
 	int num_stripes;
 	int sub_stripes;
 	int verified_stripes; /* For mount time dev extent verification */