Btrfs: remove btrfs_sector_sum structure

Using the structure btrfs_sector_sum to keep the checksum value is
unnecessary, because the extents that btrfs_sector_sum points to are
continuous, we can find out the expected checksums by btrfs_ordered_sum's
bytenr and the offset, so we can remove btrfs_sector_sum's bytenr. After
removing bytenr, there is only one member in the structure, so it makes
no sense to keep the structure, just remove it, and use a u32 array to
store the checksum value.

By this change, we don't use the while loop to get the checksums one by
one. Now, we can get several checksum value at one time, it improved the
performance by ~74% on my SSD (31MB/s -> 54MB/s).

test command:
 # dd if=/dev/zero of=/mnt/btrfs/file0 bs=1M count=1024 oflag=sync

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 8 insertions, 11 deletions

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 665c640e3ea6..81369827e514 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -1032,7 +1032,6 @@ int btrfs_find_ordered_sum(struct inode *inode, u64 offset, u64 disk_bytenr,
                            u32 *sum, int len)
 {
         struct btrfs_ordered_sum *ordered_sum;
-        struct btrfs_sector_sum *sector_sums;
         struct btrfs_ordered_extent *ordered;
         struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;
         unsigned long num_sectors;
@@ -1050,18 +1049,16 @@ int btrfs_find_ordered_sum(struct inode *inode, u64 offset, u64 disk_bytenr,
                     disk_bytenr < ordered_sum->bytenr + ordered_sum->len) {
                         i = (disk_bytenr - ordered_sum->bytenr) >>
                             inode->i_sb->s_blocksize_bits;
-                        sector_sums = ordered_sum->sums + i;
                         num_sectors = ordered_sum->len >>
                                       inode->i_sb->s_blocksize_bits;
-                        for (; i < num_sectors; i++) {
-                                if (sector_sums[i].bytenr == disk_bytenr) {
-                                        sum[index] = sector_sums[i].sum;
-                                        index++;
-                                        if (index == len)
-                                                goto out;
-                                        disk_bytenr += sectorsize;
-                                }
-                        }
+                        num_sectors = min_t(int, len - index, num_sectors - i);
+                        memcpy(sum + index, ordered_sum->sums + i,
+                               num_sectors);
+
+                        index += (int)num_sectors;
+                        if (index == len)
+                                goto out;
+                        disk_bytenr += num_sectors * sectorsize;
                 }
         }
 out: