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, 8 insertions, 8 deletions

diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index 79438cdd604e..1db4395df21d 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -949,9 +949,10 @@ static struct page *page_in_rbio(struct btrfs_raid_bio *rbio,
  * number of pages we need for the entire stripe across all the
  * drives
  */
-static unsigned long rbio_nr_pages(unsigned long stripe_len, int nr_stripes)
+static unsigned long rbio_nr_pages(u32 stripe_len, int nr_stripes)
 {
-	return DIV_ROUND_UP(stripe_len, PAGE_SIZE) * nr_stripes;
+	ASSERT(IS_ALIGNED(stripe_len, PAGE_SIZE));
+	return (stripe_len >> PAGE_SHIFT) * nr_stripes;
 }
 
 /*
@@ -960,13 +961,13 @@ static unsigned long rbio_nr_pages(unsigned long stripe_len, int nr_stripes)
  */
 static struct btrfs_raid_bio *alloc_rbio(struct btrfs_fs_info *fs_info,
 					 struct btrfs_io_context *bioc,
-					 u64 stripe_len)
+					 u32 stripe_len)
 {
 	struct btrfs_raid_bio *rbio;
 	int nr_data = 0;
 	int real_stripes = bioc->num_stripes - bioc->num_tgtdevs;
 	int num_pages = rbio_nr_pages(stripe_len, real_stripes);
-	int stripe_npages = DIV_ROUND_UP(stripe_len, PAGE_SIZE);
+	int stripe_npages = stripe_len >> PAGE_SHIFT;
 	void *p;
 
 	rbio = kzalloc(sizeof(*rbio) +
@@ -1691,8 +1692,7 @@ static void btrfs_raid_unplug(struct blk_plug_cb *cb, bool from_schedule)
 /*
  * our main entry point for writes from the rest of the FS.
  */
-int raid56_parity_write(struct bio *bio, struct btrfs_io_context *bioc,
-			u64 stripe_len)
+int raid56_parity_write(struct bio *bio, struct btrfs_io_context *bioc, u32 stripe_len)
 {
 	struct btrfs_fs_info *fs_info = bioc->fs_info;
 	struct btrfs_raid_bio *rbio;
@@ -2089,7 +2089,7 @@ cleanup:
  * of the drive.
  */
 int raid56_parity_recover(struct bio *bio, struct btrfs_io_context *bioc,
-			  u64 stripe_len, int mirror_num, int generic_io)
+			  u32 stripe_len, int mirror_num, int generic_io)
 {
 	struct btrfs_fs_info *fs_info = bioc->fs_info;
 	struct btrfs_raid_bio *rbio;
@@ -2195,7 +2195,7 @@ static void read_rebuild_work(struct btrfs_work *work)
 
 struct btrfs_raid_bio *raid56_parity_alloc_scrub_rbio(struct bio *bio,
 				struct btrfs_io_context *bioc,
-				u64 stripe_len, struct btrfs_device *scrub_dev,
+				u32 stripe_len, struct btrfs_device *scrub_dev,
 				unsigned long *dbitmap, int stripe_nsectors)
 {
 	struct btrfs_fs_info *fs_info = bioc->fs_info;