Commit fe5ecbe8 authored by David Sterba's avatar David Sterba
Browse files

btrfs: precalculate checksums per leaf once 



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 After the 64bit division has been replaced
by shift, there's still a calculation done each time the function is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 constant 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 the 32bit type.

Replace the open-coded rounding up with a macro that internally handles
the 64bit division and as it's now a short function, make it static
inline (slight code increase, slight stack usage reduction).

Reviewed-by: default avatarJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 22b6331d

fs/btrfs/ctree.h

+12 −1
Original line number Diff line number Diff line
@@ -938,6 +938,7 @@ struct btrfs_fs_info { 
	/* ilog2 of sectorsize, use to avoid 64bit division */

	u32 sectorsize_bits;

	u32 csum_size;

	u32 csums_per_leaf;

	u32 stripesize;



	/* Block groups and devices containing active swapfiles. */
@@ -2525,7 +2526,17 @@ int btrfs_get_extent_inline_ref_type(const struct extent_buffer *eb, 
				     enum btrfs_inline_ref_type is_data);

u64 hash_extent_data_ref(u64 root_objectid, u64 owner, u64 offset);



u64 btrfs_csum_bytes_to_leaves(struct btrfs_fs_info *fs_info, u64 csum_bytes);

/*

 * Take the number of bytes to be checksummmed and figure out how many leaves

 * it would require to store the csums for that many bytes.

 */

static inline u64 btrfs_csum_bytes_to_leaves(

			const struct btrfs_fs_info *fs_info, u64 csum_bytes)

{

	const u64 num_csums = csum_bytes >> fs_info->sectorsize_bits;



	return DIV_ROUND_UP_ULL(num_csums, fs_info->csums_per_leaf);

}



/*

 * Use this if we would be adding new items, as we could split nodes as we cow

fs/btrfs/disk-io.c

+1 −0
Original line number Diff line number Diff line
@@ -3081,6 +3081,7 @@ 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;



	/*

fs/btrfs/extent-tree.c

+0 −19
Original line number Diff line number Diff line
@@ -2132,25 +2132,6 @@ static u64 find_middle(struct rb_root *root) 
}

#endif



/*

 * Takes the number of bytes to be csumm'ed and figures out how many leaves it

 * would require to store the csums for that many bytes.

 */

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;

}



/*

 * this starts processing the delayed reference count updates and

 * extent insertions we have queued up so far.  count can be