Commits
Dave Chinner committed 610125ab1e4
xfs: speed up directory bestfree block scanning When running a "create millions inodes in a directory" test recently, I noticed we were spending a huge amount of time converting freespace block headers from disk format to in-memory format: 31.47% [kernel] [k] xfs_dir2_node_addname 17.86% [kernel] [k] xfs_dir3_free_hdr_from_disk 3.55% [kernel] [k] xfs_dir3_free_bests_p We shouldn't be hitting the best free block scanning code so hard when doing sequential directory creates, and it turns out there's a highly suboptimal loop searching the the best free array in the freespace block - it decodes the block header before checking each entry inside a loop, instead of decoding the header once before running the entry search loop. This makes a massive difference to create rates. Profile now looks like this: 13.15% [kernel] [k] xfs_dir2_node_addname 3.52% [kernel] [k] xfs_dir3_leaf_check_int 3.11% [kernel] [k] xfs_log_commit_cil And the wall time/average file create rate differences are just as stark: create time(sec) / rate (files/s) File count vanilla patched 10k 0.41 / 24.3k 0.42 / 23.8k 20k 0.74 / 27.0k 0.76 / 26.3k 100k 3.81 / 26.4k 3.47 / 28.8k 200k 8.58 / 23.3k 7.19 / 27.8k 1M 85.69 / 11.7k 48.53 / 20.6k 2M 280.31 / 7.1k 130.14 / 15.3k The larger the directory, the bigger the performance improvement. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>