btrfs: improve the batch insertion of delayed items
When we insert the delayed items of an inode, which corresponds to the directory index keys for a directory (key type BTRFS_DIR_INDEX_KEY), we do the following: 1) Pick the first delayed item from the rbtree and insert it into the fs/subvolume btree, using btrfs_insert_empty_item() for that; 2) Without releasing the path returned by btrfs_insert_empty_item(), keep collecting as many consecutive delayed items from the rbtree as possible, as long as each one's BTRFS_DIR_INDEX_KEY key is the immediate successor of the previously picked item and as long as they fit in the available space of the leaf the path points to; 3) Then insert all the collected items into the leaf; 4) Release the reserve metadata space for each collected item and release each item (implies deleting from the rbtree); 5) Unlock the path. While this is much better than inserting items one by one, it can be improved in a few aspects: 1) Instead of adding items based on the remaining free space of the leaf, collect as many items that can fit in a leaf and bulk insert them. This results in less and larger batches, reducing the total amount of time to insert the delayed items. For example when adding 100K files to a directory, we ended up creating 1658 batches with very variable sizes ranging from 1 item to 118 items, on a filesystem with a node/leaf size of 16K. After this change, we end up with 839 batches, with the vast majority of them having exactly 120 items; 2) We do the search for more items to batch, by iterating the rbtree, while holding a write lock on the leaf; 3) While still holding the leaf locked, we are releasing the reserved metadata for each item and then deleting each item, keeping a write lock on the leaf for longer than necessary. Releasing the delayed items one by one can take a significant amount of time, because deleting them from the rbtree can often be a bit slow when the deletion results in rebalancing the rbtree. So change this so that we try to create larger batches, with a total item size up to the maximum a leaf can support, and by unlocking the leaf immediately after inserting the items, releasing the reserved metadata space of each item and releasing each item without holding the write lock on the leaf. The following script that runs fs_mark was used to test this change: $ cat test.sh #!/bin/bash DEV=/dev/nvme0n1 MNT=/mnt/nvme0n1 MOUNT_OPTIONS="-o ssd" MKFS_OPTIONS="-m single -d single" FILES=1000000 THREADS=16 FILE_SIZE=0 echo "performance" | tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor umount $DEV &> /dev/null mkfs.btrfs -f $MKFS_OPTIONS $DEV mount $MOUNT_OPTIONS $DEV $MNT OPTS="-S 0 -L 5 -n $FILES -s $FILE_SIZE -t 16" for ((i = 1; i <= $THREADS; i++)); do OPTS="$OPTS -d $MNT/d$i" done fs_mark $OPTS umount $MNT It was run on machine with 12 cores, 64G of ram, using a NVMe device and using a non-debug kernel config (Debian's default config). Results before this change: FSUse% Count Size Files/sec App Overhead 1 16000000 0 76182.1 72223046 3 32000000 0 62746.9 80776528 5 48000000 0 77029.0 93022381 6 64000000 0 73691.6 95251075 8 80000000 0 66288.0 85089634 Results after this change: FSUse% Count Size Files/sec App Overhead 1 16000000 0 79049.5 (+3.7%) 69700824 3 32000000 0 65248.9 (+3.9%) 80583693 5 48000000 0 77991.4 (+1.2%) 90040908 6 64000000 0 75096.8 (+1.9%) 89862241 8 80000000 0 66926.8 (+1.0%) 84429169 Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Please register or sign in to comment