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, 3 insertions, 4 deletions

diff --git a/fs/btrfs/raid56.h b/fs/btrfs/raid56.h
index 72c00fc284b5..006b4741e5c1 100644
--- a/fs/btrfs/raid56.h
+++ b/fs/btrfs/raid56.h
@@ -31,15 +31,14 @@ struct btrfs_raid_bio;
 struct btrfs_device;
 
 int raid56_parity_recover(struct bio *bio, struct btrfs_io_context *bioc,
-			  u64 stripe_len, int mirror_num, int generic_io);
-int raid56_parity_write(struct bio *bio, struct btrfs_io_context *bioc,
-			u64 stripe_len);
+			  u32 stripe_len, int mirror_num, int generic_io);
+int raid56_parity_write(struct bio *bio, struct btrfs_io_context *bioc, u32 stripe_len);
 
 void raid56_add_scrub_pages(struct btrfs_raid_bio *rbio, struct page *page,
 			    u64 logical);
 
 struct btrfs_raid_bio *raid56_parity_alloc_scrub_rbio(struct bio *bio,
-				struct btrfs_io_context *bioc, u64 stripe_len,
+				struct btrfs_io_context *bioc, u32 stripe_len,
 				struct btrfs_device *scrub_dev,
 				unsigned long *dbitmap, int stripe_nsectors);
 void raid56_parity_submit_scrub_rbio(struct btrfs_raid_bio *rbio);