tests/btrfs/181

#! /bin/bash
# SPDX-License-Identifier: GPL-2.0
# Copyright (C) 2019 SUSE Linux Products GmbH. All Rights Reserved.
#
# FS QA Test 181
#
# Test if btrfs will commit too many transactions for nothing and cause
# performance regression during balance.
#
# This bug is going to be fixed by a patch for kernel title
# "btrfs: don't end the transaction for delayed refs in throttle"
#
. ./common/preamble
_begin_fstest auto quick balance

. ./common/filter

_require_scratch
_require_btrfs_command inspect-internal dump-super

_scratch_mkfs > /dev/null

_scratch_mount

nr_files=1024

get_super_gen()
{
	local ret=$($BTRFS_UTIL_PROG inspect dump-super "$SCRATCH_DEV" |\
		grep ^generation | $AWK_PROG '{print $2}')
	if [ -z $ret ]; then
		_fail "failed to get super block generation"
	fi
	echo "$ret"
}

$BTRFS_UTIL_PROG subvolume create "$SCRATCH_MNT/subvol" > /dev/null

# Create some small files to take up enough metadata reserved space
for ((i = 0; i < $nr_files; i++)) do
	_pwrite_byte 0xcd 0 1K "$SCRATCH_MNT/subvol/file_$i" > /dev/null
done

# Commit the fs so we can get a stable super generation
sync

before_gen=$(get_super_gen)

_run_btrfs_balance_start -m $SCRATCH_MNT >> $seqres.full

after_gen=$(get_super_gen)

# Since the fs is pretty small, we should have only 1 small metadata chunk and
# one tiny system chunk.
# Relocating such small chunks only needs 6 commits for each, thus 12 commits for
# 2 chunks.
# Here we use 10x the theoretic value as threshold.
theoretic_gen=$(( 6 * 2 ))
threshold_gen=$(( 10 * $theoretic_gen ))
if [ $(( $after_gen - $before_gen )) -gt 120 ]; then
	echo "balance committed too many transactions"
	echo "super generation before balance: ${before_gen}"
	echo "super generation after balance:  ${after_gen}"
	echo "super generation difference:     $((after_gen - before_gen))"
	echo "theoretic generation difference: ${theoretic_gen}"
	echo "threshold generation difference: ${threshold_gen}"
fi

echo "super generation before balance: ${before_gen}" >> $seqres.full
echo "super generation after balance:  ${after_gen}" >> $seqres.full
echo "super generation difference:     $((after_gen - before_gen))" >> $seqres.full
echo "theoretic generation difference: ${theoretic_gen}" >> $seqres.full
echo "threshold generation difference: ${threshold_gen}" >> $seqres.full

# success, all done
echo "Silence is golden"

status=0
exit