linux-kernel - Re: [PATCH v5 11/12] ext4: Test atomic writes allocation and write codepaths with bigalloc

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Message-ID: <001c5111-84c8-4bb0-951a-cc51587479be@oracle.com>
Date: Tue, 2 Sep 2025 16:54:48 +0100
From: John Garry <john.g.garry@...cle.com>
To: Ojaswin Mujoo <ojaswin@...ux.ibm.com>, Zorro Lang <zlang@...hat.com>,
        fstests@...r.kernel.org
Cc: Ritesh Harjani <ritesh.list@...il.com>, djwong@...nel.org, tytso@....edu,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH v5 11/12] ext4: Test atomic writes allocation and write
 codepaths with bigalloc

On 22/08/2025 09:02, Ojaswin Mujoo wrote:
> From: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
> 
> This test does a parallel RWF_ATOMIC IO on a multiple truncated files in
> a small FS. The idea is to stress ext4 allocator to ensure we are able
> to handle low space scenarios correctly with atomic writes. We brute
> force this for different blocksize and clustersizes and after each
> iteration we ensure the data was not torn or corrupted using fio crc
> verification.
> 
> Note that in this test we use overlapping atomic writes of same io size.
> Although serializing racing writes is not guaranteed for RWF_ATOMIC,
> NVMe and SCSI provide this guarantee as an inseparable feature to
> power-fail atomicity. Keeping the iosize as same also ensures that ext4
> doesn't tear the write due to racing ioend unwritten conversion.
> 
> The value of this test is that we make sure the RWF_ATOMIC is handled
> correctly by ext4 as well as test that the block layer doesn't split or
> only generate multiple bios for an atomic write.
> 
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
> Reviewed-by: Darrick J. Wong <djwong@...nel.org>
> Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> ---
>   tests/ext4/062     | 203 +++++++++++++++++++++++++++++++++++++++++++++
>   tests/ext4/062.out |   2 +
>   2 files changed, 205 insertions(+)
>   create mode 100755 tests/ext4/062
>   create mode 100644 tests/ext4/062.out
> 
> diff --git a/tests/ext4/062 b/tests/ext4/062
> new file mode 100755
> index 00000000..d48f69d3
> --- /dev/null
> +++ b/tests/ext4/062
> @@ -0,0 +1,203 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2025 IBM Corporation. All Rights Reserved.
> +#
> +# FS QA Test 062
> +#
> +# This test does a parallel RWF_ATOMIC IO on a multiple truncated files in a
> +# small FS. The idea is to stress ext4 allocator to ensure we are able to
> +# handle low space scenarios correctly with atomic writes.. We brute force this
> +# for all possible blocksize and clustersizes and after each iteration we
> +# ensure the data was not torn or corrupted using fio crc verification.
> +#
> +# Note that in this test we use overlapping atomic writes of same io size.
> +# Although serializing racing writes is not guaranteed for RWF_ATOMIC, NVMe and
> +# SCSI provide this guarantee as an inseparable feature to power-fail
> +# atomicity. Keeping the iosize as same also ensures that ext4 doesn't tear the
> +# write due to racing ioend unwritten conversion.
> +#
> +# The value of this test is that we make sure the RWF_ATOMIC is handled
> +# correctly by ext4 as well as test that the block layer doesn't split or only
> +# generate multiple bios for an atomic write.
> +#
> +
> +. ./common/preamble
> +. ./common/atomicwrites
> +
> +_begin_fstest auto rw stress atomicwrites
> +
> +_require_scratch_write_atomic
> +_require_aiodio
> +_require_fio_version "3.38+"
> +
> +FSSIZE=$((360*1024*1024))
> +FIO_LOAD=$(($(nproc) * LOAD_FACTOR))
> +
> +# Calculate bs as per bdev atomic write units.
> +bdev_awu_min=$(_get_atomic_write_unit_min $SCRATCH_DEV)
> +bdev_awu_max=$(_get_atomic_write_unit_max $SCRATCH_DEV)
> +bs=$(_max 4096 "$bdev_awu_min")
> +
> +function create_fio_configs()
> +{
> +	local bsize=$1
> +	create_fio_aw_config $bsize
> +	create_fio_verify_config $bsize
> +}
> +
> +function create_fio_verify_config()
> +{
> +	local bsize=$1
> +cat >$fio_verify_config <<EOF
> +	[global]
> +	direct=1
> +	ioengine=libaio
> +	rw=read
> +	bs=$bsize
> +	fallocate=truncate
> +	size=$((FSSIZE / 12))
> +	iodepth=$FIO_LOAD
> +	numjobs=$FIO_LOAD
> +	group_reporting=1
> +	atomic=1
> +
> +	verify_only=1
> +	verify_state_save=0
> +	verify=crc32c
> +	verify_fatal=1
> +	verify_write_sequence=0
> +
> +	[verify-job1]
> +	filename=$SCRATCH_MNT/testfile-job1
> +
> +	[verify-job2]
> +	filename=$SCRATCH_MNT/testfile-job2
> +
> +	[verify-job3]
> +	filename=$SCRATCH_MNT/testfile-job3
> +
> +	[verify-job4]
> +	filename=$SCRATCH_MNT/testfile-job4
> +
> +	[verify-job5]
> +	filename=$SCRATCH_MNT/testfile-job5
> +
> +	[verify-job6]
> +	filename=$SCRATCH_MNT/testfile-job6
> +
> +	[verify-job7]
> +	filename=$SCRATCH_MNT/testfile-job7
> +
> +	[verify-job8]
> +	filename=$SCRATCH_MNT/testfile-job8

do you really need multiple jobs for verify?