From: Darrick J. Wong Date: Mon, 10 Nov 2025 18:26:32 +0000 (-0800) Subject: generic/778: fix severe performance problems X-Git-Tag: v2025.11.18~11 X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=252d25fb9efdcc36af734de270698bc6db918939;p=xfstests-dev.git generic/778: fix severe performance problems This test takes 4800s to run, which is horrible. AFAICT it starts out by timing how much can be written atomically to a new file in 0.2 seconds, then scales up the file size by 3x. On not very fast storage, this can result in file_size being set to ~250MB on a 4k fsblock filesystem. That's about 64,000 blocks. The next thing this test does is try to create a file of that size (250MB) of alternating written and unwritten blocks. For some reason, it sets up this file by invoking xfs_io 64,000 times to write small amounts of data, which takes 3+ minutes on the author's system because exec overhead is pretty high when you do that. As a result, one loop through the test takes almost 4 minutes. The test loops 20 times, so it runs for 80 minutes(!!) which is a really long time. So the first thing we do is observe that the giant slow loop is being run as a single thread on an empty filesystem. Most of the time the allocator generates a mostly physically contiguous file. We could fallocate the whole file instead of fallocating one block every other time through the loop. This halves the setup time. Next, we can also stuff the remaining pwrite commands into a bash array and only invoke xfs_io once every 128x through the loop. This amortizes the xfs_io startup time, which reduces the test loop runtime to about 20 seconds. Finally, replace the 20x loop with a _soak_loop_running 5x loop because 5 seems like enough. Anyone who wants more can set TIME_FACTOR or SOAK_DURATION to get more intensive testing. On my system this cuts the runtime to 75 seconds. Cc: fstests@vger.kernel.org # v2025.10.20 Fixes: ca954527ff9d97 ("generic: Add sudden shutdown tests for multi block atomic writes") Signed-off-by: Darrick J. Wong Reviewed-by: Christoph Hellwig Signed-off-by: Zorro Lang --- diff --git a/tests/generic/778 b/tests/generic/778 index 8cb1d8d4..7cfabc3a 100755 --- a/tests/generic/778 +++ b/tests/generic/778 @@ -42,22 +42,28 @@ atomic_write_loop() { # Due to sudden shutdown this can produce errors so just # redirect them to seqres.full $XFS_IO_PROG -c "open -fsd $testfile" -c "pwrite -S 0x61 -DA -V1 -b $size $off $size" >> /dev/null 2>>$seqres.full - echo "Written to offset: $off" >> $tmp.aw - off=$((off + $size)) + echo "Written to offset: $((off + size))" >> $tmp.aw + off=$((off + size)) done } start_atomic_write_and_shutdown() { atomic_write_loop & awloop_pid=$! + local max_loops=100 local i=0 - # Wait for at least first write to be recorded or 10s - while [ ! -f "$tmp.aw" -a $i -le 50 ]; do i=$((i + 1)); sleep 0.2; done + # Wait for at least first write to be recorded or too much time passes + while [ ! -f "$tmp.aw" -a $i -le $max_loops ]; do + i=$((i + 1)) + sleep 0.2 + done + + cat $tmp.aw >> $seqres.full - if [[ $i -gt 50 ]] + if [[ $i -gt $max_loops ]] then - _fail "atomic write process took too long to start" + _notrun "atomic write process took too long to start" fi echo >> $seqres.full @@ -113,21 +119,34 @@ create_mixed_mappings() { local off=0 local operations=("W" "U") + test $size_bytes -eq 0 && return + + # fallocate the whole file once because preallocating single blocks + # with individual xfs_io invocations is really slow and the allocator + # usually gives out consecutive blocks anyway + $XFS_IO_PROG -f -c "falloc 0 $size_bytes" $file + + local cmds=() for ((i=0; i<$((size_bytes / blksz )); i++)); do - index=$(($i % ${#operations[@]})) - map="${operations[$index]}" - - case "$map" in - "W") - $XFS_IO_PROG -fc "pwrite -b $blksz $off $blksz" $file >> /dev/null - ;; - "U") - $XFS_IO_PROG -fc "falloc $off $blksz" $file >> /dev/null - ;; - esac + if (( i % 2 == 0 )); then + cmds+=(-c "pwrite -b $blksz $off $blksz") + fi + + # batch the write commands into larger xfs_io invocations to + # amortize the fork overhead + if [ "${#cmds[@]}" -ge 128 ]; then + $XFS_IO_PROG "${cmds[@]}" "$file" >> /dev/null + cmds=() + fi + off=$((off + blksz)) done + if [ "${#cmds[@]}" -gt 0 ]; then + $XFS_IO_PROG "${cmds[@]}" "$file" >> /dev/null + cmds=() + fi + sync $file } @@ -336,9 +355,9 @@ echo >> $seqres.full echo "# Populating expected data buffers" >> $seqres.full populate_expected_data -# Loop 20 times to shake out any races due to shutdown -for ((iter=0; iter<20; iter++)) -do +# Loop to shake out any races due to shutdown +iter=0 +while _soak_loop_running $TIME_FACTOR; do echo >> $seqres.full echo "------ Iteration $iter ------" >> $seqres.full @@ -361,6 +380,8 @@ do echo >> $seqres.full echo "# Starting shutdown torn write test for append atomic writes" >> $seqres.full test_append_torn_write + + iter=$((iter + 1)) done echo "Silence is golden"