When doing a full send we know that we are going to be reading every node
and leaf of the send root, so we benefit from enabling read ahead for the
btree.
This change enables read ahead for full send operations only, incremental
sends will have read ahead enabled in a different way by a separate patch.
The following test script was used to measure the improvement on a box
using an average, consumer grade, spinning disk and with 16GiB of RAM:
$ cat test.sh
#!/bin/bash
DEV=/dev/sdj
MNT=/mnt/sdj
MKFS_OPTIONS="--nodesize 16384" # default, just to be explicit
MOUNT_OPTIONS="-o max_inline=2048" # default, just to be explicit
mkfs.btrfs -f $MKFS_OPTIONS $DEV > /dev/null
mount $MOUNT_OPTIONS $DEV $MNT
# Create files with inline data to make it easier and faster to create
# large btrees.
add_files()
{
local total=$1
local start_offset=$2
local number_jobs=$3
local total_per_job=$(($total / $number_jobs))
echo "Creating $total new files using $number_jobs jobs"
for ((n = 0; n < $number_jobs; n++)); do
(
local start_num=$(($start_offset + $n * $total_per_job))
for ((i = 1; i <= $total_per_job; i++)); do
local file_num=$((start_num + $i))
local file_path="$MNT/file_${file_num}"
xfs_io -f -c "pwrite -S 0xab 0 2000" $file_path > /dev/null
if [ $? -ne 0 ]; then
echo "Failed creating file $file_path"
break
fi
done
) &
worker_pids[$n]=$!
done
wait ${worker_pids[@]}
sync
echo
echo "btree node/leaf count: $(btrfs inspect-internal dump-tree -t 5 $DEV | egrep '^(node|leaf) ' | wc -l)"
}
initial_file_count=500000
add_files $initial_file_count 0 4
echo
echo "Creating first snapshot..."
btrfs subvolume snapshot -r $MNT $MNT/snap1
echo
echo "Adding more files..."
add_files $((initial_file_count / 4)) $initial_file_count 4
echo
echo "Updating 1/50th of the initial files..."
for ((i = 1; i < $initial_file_count; i += 50)); do
xfs_io -c "pwrite -S 0xcd 0 20" $MNT/file_$i > /dev/null
done
echo
echo "Creating second snapshot..."
btrfs subvolume snapshot -r $MNT $MNT/snap2
umount $MNT
echo 3 > /proc/sys/vm/drop_caches
blockdev --flushbufs $DEV &> /dev/null
hdparm -F $DEV &> /dev/null
mount $MOUNT_OPTIONS $DEV $MNT
echo
echo "Testing full send..."
start=$(date +%s)
btrfs send $MNT/snap1 > /dev/null
end=$(date +%s)
echo
echo "Full send took $((end - start)) seconds"
umount $MNT
echo 3 > /proc/sys/vm/drop_caches
blockdev --flushbufs $DEV &> /dev/null
hdparm -F $DEV &> /dev/null
mount $MOUNT_OPTIONS $DEV $MNT
echo
echo "Testing incremental send..."
start=$(date +%s)
btrfs send -p $MNT/snap1 $MNT/snap2 > /dev/null
end=$(date +%s)
echo
echo "Incremental send took $((end - start)) seconds"
umount $MNT
Before this change, full send duration:
with $initial_file_count == 200000: 165 seconds
with $initial_file_count == 500000: 407 seconds
After this change, full send duration:
with $initial_file_count == 200000: 149 seconds (-10.2%)
with $initial_file_count == 500000: 353 seconds (-14.2%)
For $initial_file_count == 200000 there are 62600 nodes and leaves in the
btree of the first snapshot, while for $initial_file_count == 500000 there
are 152476 nodes and leaves. The roots were at level 2.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
19358b154f