Commit 5d13a98f authored by Chris Mason's avatar Chris Mason
Browse files

Btrfs: readahead checksums during btrfs_finish_ordered_io

This reads in blocks in the checksum btree before starting the
transaction in btrfs_finish_ordered_io.  It makes it much more likely
we'll be able to do operations inside the transaction without
needing any btree reads, which limits transaction latencies overall.
Signed-off-by: default avatarChris Mason <>
parent b9473439
......@@ -1497,6 +1497,30 @@ static int insert_reserved_file_extent(struct btrfs_trans_handle *trans,
return 0;
* helper function for btrfs_finish_ordered_io, this
* just reads in some of the csum leaves to prime them into ram
* before we start the transaction. It limits the amount of btree
* reads required while inside the transaction.
static noinline void reada_csum(struct btrfs_root *root,
struct btrfs_path *path,
struct btrfs_ordered_extent *ordered_extent)
struct btrfs_ordered_sum *sum;
u64 bytenr;
sum = list_entry(ordered_extent->, struct btrfs_ordered_sum,
bytenr = sum->sums[0].bytenr;
* we don't care about the results, the point of this search is
* just to get the btree leaves into ram
btrfs_lookup_csum(NULL, root->fs_info->csum_root, path, bytenr, 0);
/* as ordered data IO finishes, this gets called so we can finish
* an ordered extent if the range of bytes in the file it covers are
* fully written.
......@@ -1505,7 +1529,7 @@ static int btrfs_finish_ordered_io(struct inode *inode, u64 start, u64 end)
struct btrfs_root *root = BTRFS_I(inode)->root;
struct btrfs_trans_handle *trans;
struct btrfs_ordered_extent *ordered_extent;
struct btrfs_ordered_extent *ordered_extent = NULL;
struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
struct btrfs_path *path;
int compressed = 0;
......@@ -1528,13 +1552,20 @@ static int btrfs_finish_ordered_io(struct inode *inode, u64 start, u64 end)
ret = btrfs_lookup_file_extent(NULL, root, path,
start, 0);
ordered_extent = btrfs_lookup_ordered_extent(inode,
if (!list_empty(&ordered_extent->list)) {
btrfs_release_path(root, path);
reada_csum(root, path, ordered_extent);
trans = btrfs_join_transaction(root, 1);
ordered_extent = btrfs_lookup_ordered_extent(inode, start);
if (!ordered_extent)
ordered_extent = btrfs_lookup_ordered_extent(inode, start);
if (test_bit(BTRFS_ORDERED_NOCOW, &ordered_extent->flags))
goto nocow;
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