Re: [PATCH v3] generic/608: verify S_DAX is active immediately for DONTCACHE

[Xiao Yang <yangx.jy@cn.fujitsu.com>]

On 2021/2/20 0:44, XiaoLi Feng wrote:
> From: Xiaoli Feng <xifeng@redhat.com>
>
> After upstream linux patches(77573fa310d, 88149082bb8), if
> FS_XFLAG_DAX is set, DONTCACHE is also set. So S_DAX on the file

What do you mean that if FS_XFLAG_DAX is set, DONTCACHE is also set?
It seems that enabling FS_XFLAG_DAX will set DCACHE_DONTCACHE and
I_DONTCACHE automatically.

> should be active immediately once FS_XFLAG_DAX is set.
> ---
>  tests/generic/608 | 42 ++++++++++++++++++++----------------------
>  1 file changed, 20 insertions(+), 22 deletions(-)
>
> diff --git a/tests/generic/608 b/tests/generic/608
> index dd89d91c..b207602e 100755
> --- a/tests/generic/608
> +++ b/tests/generic/608
> @@ -6,7 +6,10 @@
>  # Change FS_XFLAG_DAX on an existing file and check if S_DAX on
>  # the file can take effect immediately by the following steps:
>  # 1) Stop all applications which are using the file.
> -# 2) Do drop_caches or umount & mount cycle.
> +# 2) Enable the dax flag on the file that no applications are using. 

How about the following comment:
1) When no applications are using an existing file, changing FS_XFLAG_DAX
on the file make S_DAX take effect immediately.
2) When some applications are using an existing file, changing FS_XFLAG_DAX
on the file make S_DAX take effect immediately util all applications stop
using it.

> +# The upstream commit 88149082bb8 make the S_DAX take effect 
> +# immediately because the inode is no longer cached and will re-read
> +# from disk.

Commit 77573fa310d makes S_DAX take effect immediately(i.e. don't depend
drop_caches or umount & mount cycle).
Commit 88149082bb8 is trying to resolve another bug.

>  
>  seq=`basename $0`
>  seqres=$RESULT_DIR/$seq
> @@ -36,7 +39,7 @@ _require_dax_iflag
>  _require_xfs_io_command "lsattr" "-v"
>  _require_xfs_io_command "statx" "-r"
>  
> -test_drop_caches()
> +test_caches()
>  {
>  	local t_file=$SCRATCH_MNT/testfile
>  
> @@ -49,24 +52,19 @@ test_drop_caches()
>  
>  	$XFS_IO_PROG -c 'chattr +x' $t_file
>  	_check_xflag $t_file 1
> -	_check_s_dax $t_file 0
> -
>  	# One application is using test file and check if S_DAX on
> -	# the file doesn't take effect immediately by drop_caches
> -	echo 2 > /proc/sys/vm/drop_caches
> +	# the file doesn't take effect immediately.
>  	_check_s_dax $t_file 0
>  
>  	exec 3<&-
>  
>  	# No application is using test file and check if S_DAX on
> -	# the file takes effect immediately by drop_caches
> -	echo 2 > /proc/sys/vm/drop_caches
> +	# the file takes effect immediately
>  	_check_s_dax $t_file 1
>  }
>  
> -test_cycle_mount()
> +test_nocache()
>  {
> -	local option=$1
>  	local t_dir=$SCRATCH_MNT/testdir
>  	local t_file=$t_dir/testfile
>  
> @@ -77,30 +75,30 @@ test_cycle_mount()
>  	_check_xflag $t_file 1
>  	_check_s_dax $t_file 1
>  
> -	exec 3< $t_file
> -
> -	$XFS_IO_PROG -c 'chattr -x' $t_file
> +	$XFS_IO_PROG -c 'chattr -x -R' $t_dir
>  	_check_xflag $t_file 0
> -	_check_s_dax $t_file 1
> +	_check_s_dax $t_file 0
>  
> -	exec 3<&-
> +	$XFS_IO_PROG -c 'chattr +x' $t_file
> +	# Here S_DAX on the file will take effect immediately
> +	# because of inode DONTCACHE. 
> +	_check_xflag $t_file 1
> +	_check_s_dax $t_file 1

Why do you need the extra steps?
------------------------------------
78 $XFS_IO_PROG -c 'chattr -x -R' $t_dir
79 _check_xflag $t_file 0
80 _check_s_dax $t_file 0
81
82 $XFS_IO_PROG -c 'chattr +x' $t_file
83 # Here S_DAX on the file will take effect immediately
84 # because of inode DONTCACHE.
85 _check_xflag $t_file 1
86 _check_s_dax $t_file 1
------------------------------------

Best Regards,
Xiao Yang
>  
> -	# No application is using test file and check if S_DAX on
> -	# the file takes effect immediately by umount & mount
> -	_scratch_cycle_mount "$option"
> +	$XFS_IO_PROG -c 'chattr -x' $t_file
> +	_check_xflag $t_file 0
>  	_check_s_dax $t_file 0
>  }
>  
>  do_tests()
>  {
>  	local mount_option=$1
> -	local cycle_mount_option=$2
>  
>  	_scratch_mount "$mount_option"
>  
> -	test_drop_caches
> +	test_caches
>  
> -	test_cycle_mount "$cycle_mount_option"
> +	test_nocache
>  
>  	_scratch_unmount
>  }
> @@ -108,7 +106,7 @@ do_tests()
>  _scratch_mkfs >> $seqres.full 2>&1
>  
>  # Mount with dax option
> -do_tests "-o dax=inode" "dax=inode"
> +do_tests "-o dax=inode"
>  
>  # Mount without dax option
>  export MOUNT_OPTIONS=""