Re: [PATCH] fstests: generic: add a basic cachestat test case

[Brian Foster <bfoster@redhat.com>]

On Thu, Jul 16, 2026 at 08:07:16AM +0930, Qu Wenruo wrote:
> The test case is inspired by LTP, where there is a regression on 64K
> page size systems with btrfs, that after a fsync, cachestat() still
> report dirty pages.
> 
> The test case itself is pretty simple, fill the file with a buffered write that is
> 1/2/4/8/16 page sized, call cachestat() to make sure the cached/dirtied
> number match the page number.
> 
> Then do a fsync(), and make sure the dirty page number reduced to 0
> meanwhile cached is still the same.
> 
> Link: https://bugzilla.suse.com/show_bug.cgi?id=1270397
> Reviewed-by: Anand Jain <asj@kernel.org>
> Reviewed-by: Filipe Manana <fdmanana@suse.com>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> Changelog:
> v3:
> - Use golden output to greatly simplify the test case
> 
> - Do not mkfs for each size, just remove the original file
> 
> v2:
> - Reject "sync" and "dax" mount options
>   Those mount options write back data synchronously, will screw up the
>   buffered write dirtied page reporting.
> 
> - Use AWK_PROG everywhere.
> 
> - Remove the unnecessary redirection for fsync
> ---

Nice. Thanks for the tweaks!

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  tests/generic/798     | 39 +++++++++++++++++++++++++++++++++++++++
>  tests/generic/798.out | 16 ++++++++++++++++
>  2 files changed, 55 insertions(+)
>  create mode 100755 tests/generic/798
>  create mode 100644 tests/generic/798.out
> 
> diff --git a/tests/generic/798 b/tests/generic/798
> new file mode 100755
> index 00000000..0fe37646
> --- /dev/null
> +++ b/tests/generic/798
> @@ -0,0 +1,39 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2026 SUSE S.A.  All Rights Reserved.
> +#
> +# FS QA Test 798
> +#
> +# Basic tests for cachestat()
> +#
> +. ./common/preamble
> +_begin_fstest auto quick
> +
> +_require_xfs_io_command "cachestat"
> +_require_scratch
> +# Any mount option that writes data back synchronously should be rejected.
> +# Or it will screw up the dirtied page reporting for buffered writes.
> +_exclude_scratch_mount_option "dax"
> +_exclude_scratch_mount_option "sync"
> +
> +pagesize=$(_get_page_size)
> +
> +_scratch_mkfs > /dev/null
> +_scratch_mount
> +
> +for num_page in 1 2 4 8 16; do
> +	size=$(($pagesize * $num_page))
> +
> +	echo "=== Test with $num_page pages ==="
> +
> +	rm -f $SCRATCH_MNT/foobar
> +	$XFS_IO_PROG -f -c "pwrite -b $pagesize 0 $size" $SCRATCH_MNT/foobar > /dev/null
> +	# Basic cached number reporting
> +	$XFS_IO_PROG -c "cachestat 0 $size" $SCRATCH_MNT/foobar
> +
> +	# Test dirty page number reporting after a fsync.
> +	$XFS_IO_PROG -c "fsync" -c "cachestat 0 $size" $SCRATCH_MNT/foobar
> +done
> +
> +_scratch_unmount
> +_exit 0
> diff --git a/tests/generic/798.out b/tests/generic/798.out
> new file mode 100644
> index 00000000..ca6ead3c
> --- /dev/null
> +++ b/tests/generic/798.out
> @@ -0,0 +1,16 @@
> +QA output created by 798
> +=== Test with 1 pages ===
> +Cached: 1, Dirty: 1, Writeback: 0, Evicted: 0, Recently Evicted: 0
> +Cached: 1, Dirty: 0, Writeback: 0, Evicted: 0, Recently Evicted: 0
> +=== Test with 2 pages ===
> +Cached: 2, Dirty: 2, Writeback: 0, Evicted: 0, Recently Evicted: 0
> +Cached: 2, Dirty: 0, Writeback: 0, Evicted: 0, Recently Evicted: 0
> +=== Test with 4 pages ===
> +Cached: 4, Dirty: 4, Writeback: 0, Evicted: 0, Recently Evicted: 0
> +Cached: 4, Dirty: 0, Writeback: 0, Evicted: 0, Recently Evicted: 0
> +=== Test with 8 pages ===
> +Cached: 8, Dirty: 8, Writeback: 0, Evicted: 0, Recently Evicted: 0
> +Cached: 8, Dirty: 0, Writeback: 0, Evicted: 0, Recently Evicted: 0
> +=== Test with 16 pages ===
> +Cached: 16, Dirty: 16, Writeback: 0, Evicted: 0, Recently Evicted: 0
> +Cached: 16, Dirty: 0, Writeback: 0, Evicted: 0, Recently Evicted: 0
> -- 
> 2.51.2
>