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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 <chris.mason@oracle.com>
parent b9473439

fs/btrfs/inode.c

+33 −2
Original line number Diff line number Diff line
@@ -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->list.next, struct btrfs_ordered_sum,

			 list);

	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;
@@ -1528,12 +1552,19 @@ static int btrfs_finish_ordered_io(struct inode *inode, u64 start, u64 end) 
			ret = btrfs_lookup_file_extent(NULL, root, path,

						       inode->i_ino,

						       start, 0);

			ordered_extent = btrfs_lookup_ordered_extent(inode,

								     start);

			if (!list_empty(&ordered_extent->list)) {

				btrfs_release_path(root, path);

				reada_csum(root, path, ordered_extent);

			}

			btrfs_free_path(path);

		}

	}



	trans = btrfs_join_transaction(root, 1);



	if (!ordered_extent)

		ordered_extent = btrfs_lookup_ordered_extent(inode, start);

	BUG_ON(!ordered_extent);

	if (test_bit(BTRFS_ORDERED_NOCOW, &ordered_extent->flags))