[PATCH 05/10] btrfs: precalculate checksums per leaf once

[David Sterba <dsterba@suse.com>]

btrfs_csum_bytes_to_leaves shows up in system profiles, which makes it a
candidate for optimizations. After the 64bit division has been replaced
by shift, there's still a calculation done each time the function is
called: checksums per leaf.

As this is a constanat value for the entire filesystem lifetime, we
can calculate it once at mount time and reuse. This also allows to
reduce the division to 64bit/32bit as we know the constant will always
fit to 32bit type.

Replace the open-coded rounding up with a macro that internally handles
the 64bit division.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/ctree.h       | 1 +
 fs/btrfs/disk-io.c     | 1 +
 fs/btrfs/extent-tree.c | 9 +--------
 3 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 1f2162fc1daa..8c4cd79b2810 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -933,6 +933,7 @@ struct btrfs_fs_info {
 	u32 sectorsize;
 	u32 sectorsize_bits;
 	u32 csum_size;
+	u32 csums_per_leaf;
 	u32 stripesize;
 
 	/* Block groups and devices containing active swapfiles. */
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 25dbdfa8bc4b..f870e252aa37 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3079,6 +3079,7 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	fs_info->sectorsize = sectorsize;
 	fs_info->sectorsize_bits = ilog2(sectorsize);
 	fs_info->csum_size = btrfs_super_csum_size(disk_super);
+	fs_info->csums_per_leaf = BTRFS_MAX_ITEM_SIZE(fs_info) / fs_info->csum_size;
 	fs_info->stripesize = stripesize;
 
 	/*
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 29ac97248942..81440a0ba106 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2138,17 +2138,10 @@ static u64 find_middle(struct rb_root *root)
  */
 u64 btrfs_csum_bytes_to_leaves(struct btrfs_fs_info *fs_info, u64 csum_bytes)
 {
-	u64 csum_size;
-	u64 num_csums_per_leaf;
 	u64 num_csums;
 
-	csum_size = BTRFS_MAX_ITEM_SIZE(fs_info);
-	num_csums_per_leaf = div64_u64(csum_size,
-			(u64)btrfs_super_csum_size(fs_info->super_copy));
 	num_csums = csum_bytes >> fs_info->sectorsize_bits;
-	num_csums += num_csums_per_leaf - 1;
-	num_csums = div64_u64(num_csums, num_csums_per_leaf);
-	return num_csums;
+	return DIV_ROUND_UP_ULL(num_csums, fs_info->csums_per_leaf);
 }
 
 /*
-- 
2.25.0