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, 7 insertions, 13 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 6ab1b71a5df0..ba1e7f1b9a72 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6313,7 +6313,7 @@ int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, struct extent_map *em,
 	u64 offset;
 	u64 stripe_offset;
 	u64 stripe_nr;
-	u64 stripe_len;
+	u32 stripe_len;
 	u64 raid56_full_stripe_start = (u64)-1;
 	int data_stripes;
 
@@ -6324,19 +6324,13 @@ int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, struct extent_map *em,
 	offset = logical - em->start;
 	/* Len of a stripe in a chunk */
 	stripe_len = map->stripe_len;
-	/* Stripe where this block falls in */
-	stripe_nr = div64_u64(offset, stripe_len);
-	/* Offset of stripe in the chunk */
-	stripe_offset = stripe_nr * stripe_len;
-	if (offset < stripe_offset) {
-		btrfs_crit(fs_info,
-"stripe math has gone wrong, stripe_offset=%llu offset=%llu start=%llu logical=%llu stripe_len=%llu",
-			stripe_offset, offset, em->start, logical, stripe_len);
-		return -EINVAL;
-	}
+	/*
+	 * Stripe_nr is where this block falls in
+	 * stripe_offset is the offset of this block in its stripe.
+	 */
+	stripe_nr = div64_u64_rem(offset, stripe_len, &stripe_offset);
+	ASSERT(stripe_offset < U32_MAX);
 
-	/* stripe_offset is the offset of this block in its stripe */
-	stripe_offset = offset - stripe_offset;
 	data_stripes = nr_data_stripes(map);
 
 	/* Only stripe based profiles needs to check against stripe length. */