Message-ID: <5ECF7CD3.20409@cn.fujitsu.com>
Date:   Thu, 28 May 2020 16:56:51 +0800
From:   Xiao Yang <yangx.jy@...fujitsu.com>
To:     Ira Weiny <ira.weiny@...el.com>
CC:     <linux-ext4@...r.kernel.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Eric Biggers <ebiggers@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4 6/8] fs/ext4: Make DAX mount option a tri-state

On 2020/5/28 7:50, Ira Weiny wrote:
> On Wed, May 27, 2020 at 01:54:54PM +0800, Xiao Yang wrote:
>> On 2020/5/22 3:13, ira.weiny@...el.com wrote:
>>> From: Ira Weiny<ira.weiny@...el.com>
>>>
>>> We add 'always', 'never', and 'inode' (default).  '-o dax' continues to
>>> operate the same which is equivalent to 'always'.  This new
>>> functionality is limited to ext4 only.
>>>
>>> Specifically we introduce a 2nd DAX mount flag EXT4_MOUNT2_DAX_NEVER and set
>>> it and EXT4_MOUNT_DAX_ALWAYS appropriately for the mode.
>>>
>>> We also force EXT4_MOUNT2_DAX_NEVER if !CONFIG_FS_DAX.
>>>
>>> Finally, EXT4_MOUNT2_DAX_INODE is used solely to detect if the user
>>> specified that option for printing.
>> Hi Ira,
>>
>> I have two questions when reviewing this patch:
>> 1) After doing mount with the same dax=inode option, ext4/xfs shows
>> differnt output(i.e. xfs doesn't print 'dax=inode'):
>> ---------------------------------------------------
>> # mount -o dax=inode /dev/pmem0 /mnt/xfstests/test/
>> # mount | grep pmem0
>> /dev/pmem0 on /mnt/xfstests/test type ext4 (rw,relatime,seclabel,dax=inode)
>>
>> # mount -odax=inode /dev/pmem1 /mnt/xfstests/scratch/
>> # mount | grep pmem1
>> /dev/pmem1 on /mnt/xfstests/scratch type xfs
>> (rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota)
>> ----------------------------------------------------
>> Is this expected output? why don't unify the output?
>
> Correct. dax=inode is the default.  xfs treats that default the same whether
> you specify it on the command line or not.
>
> For ext4 Jan specifically asked that if the user specified dax=inode on the
> command line that it be printed on the mount options.  If you don't specify
> anything then dax=inode is in effect but ext4 will not print anything.
>
> I had the behavior the same as XFS originally but Jan wanted it this way.  The
> XFS behavior is IMO better and is what the new mount infrastructure gives by
> default.
Hi Ira,

Could we unify the output?  It is strange for me to use differnt output 
on ext4 and xfs.

>
>>
>> 2) Do mount without dax and mount with -odax=inode have the same behavior?
>
> Yes.
>
>> ---------------------------------------------------
>> # mount /dev/pmem0 /mnt/xfstests/test/
>> # mount | grep pmem0
>> /dev/pmem0 on /mnt/xfstests/test type ext4 (rw,relatime,seclabel)
>> # umount /mnt/xfstests/test
>> # mount -odax=inode /dev/pmem0 /mnt/xfstests/test/
>> # mount | grep pmem0
>> /dev/pmem0 on /mnt/xfstests/test type ext4 (rw,relatime,seclabel,dax=inode
>> ---------------------------------------------------
>
> These are the same behavior.  But because you specified the option it was
> echoed in the second output.

Got it, thanks for your explanation.

>
>>
>> BTW: I focus on the support of per-file/directory DAX operations recently.
>>
>>>
>>> Reviewed-by: Jan Kara<jack@...e.cz>
>>> Signed-off-by: Ira Weiny<ira.weiny@...el.com>
>>>
>>> ---
>>> Changes from V1:
>>> 	Fix up mounting options to only show an option if specified
>>> 	Fix remount to prevent dax changes
>>> 	Isolate behavior to ext4 only
>>>
>>> Changes from RFC:
>>> 	Combine remount check for DAX_NEVER with DAX_ALWAYS
>>> 	Update ext4_should_enable_dax()
>>> ---
>>>    fs/ext4/ext4.h  |  2 ++
>>>    fs/ext4/inode.c |  2 ++
>>>    fs/ext4/super.c | 67 +++++++++++++++++++++++++++++++++++++++++--------
>>>    3 files changed, 61 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>>> index f5291693ce6e..65ffb831b2b9 100644
>>> --- a/fs/ext4/ext4.h
>>> +++ b/fs/ext4/ext4.h
>>> @@ -1168,6 +1168,8 @@ struct ext4_inode_info {
>>>    						      blocks */
>>>    #define EXT4_MOUNT2_HURD_COMPAT		0x00000004 /* Support HURD-castrated
>>>    						      file systems */
>>> +#define EXT4_MOUNT2_DAX_NEVER		0x00000008 /* Do not allow Direct Access */
>>> +#define EXT4_MOUNT2_DAX_INODE		0x00000010 /* For printing options only */
>>>
>>>    #define EXT4_MOUNT2_EXPLICIT_JOURNAL_CHECKSUM	0x00000008 /* User explicitly
>>>    						specified journal checksum */
>>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>>> index 01636cf5f322..68fac9289109 100644
>>> --- a/fs/ext4/inode.c
>>> +++ b/fs/ext4/inode.c
>>> @@ -4402,6 +4402,8 @@ static bool ext4_should_enable_dax(struct inode *inode)
>>>    {
>>>    	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
>>>
>>> +	if (test_opt2(inode->i_sb, DAX_NEVER))
>>> +		return false;
>>>    	if (!S_ISREG(inode->i_mode))
>>>    		return false;
>>>    	if (ext4_should_journal_data(inode))
>>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>>> index 80eb814c47eb..5e056aa20ce9 100644
>>> --- a/fs/ext4/super.c
>>> +++ b/fs/ext4/super.c
>>> @@ -1512,7 +1512,8 @@ enum {
>>>    	Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
>>>    	Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_jqfmt_vfsv1, Opt_quota,
>>>    	Opt_noquota, Opt_barrier, Opt_nobarrier, Opt_err,
>>> -	Opt_usrquota, Opt_grpquota, Opt_prjquota, Opt_i_version, Opt_dax,
>>> +	Opt_usrquota, Opt_grpquota, Opt_prjquota, Opt_i_version,
>>> +	Opt_dax, Opt_dax_always, Opt_dax_inode, Opt_dax_never,
>>>    	Opt_stripe, Opt_delalloc, Opt_nodelalloc, Opt_warn_on_error,
>>>    	Opt_nowarn_on_error, Opt_mblk_io_submit,
>>>    	Opt_lazytime, Opt_nolazytime, Opt_debug_want_extra_isize,
>>> @@ -1579,6 +1580,9 @@ static const match_table_t tokens = {
>>>    	{Opt_nobarrier, "nobarrier"},
>>>    	{Opt_i_version, "i_version"},
>>>    	{Opt_dax, "dax"},
>>> +	{Opt_dax_always, "dax=always"},
>>> +	{Opt_dax_inode, "dax=inode"},
>>> +	{Opt_dax_never, "dax=never"},
>>>    	{Opt_stripe, "stripe=%u"},
>>>    	{Opt_delalloc, "delalloc"},
>>>    	{Opt_warn_on_error, "warn_on_error"},
>>> @@ -1726,6 +1730,7 @@ static int clear_qf_name(struct super_block *sb, int qtype)
>>>    #define MOPT_NO_EXT3	0x0200
>>>    #define MOPT_EXT4_ONLY	(MOPT_NO_EXT2 | MOPT_NO_EXT3)
>>>    #define MOPT_STRING	0x0400
>>> +#define MOPT_SKIP	0x0800
>>>
>>>    static const struct mount_opts {
>>>    	int	token;
>>> @@ -1775,7 +1780,13 @@ static const struct mount_opts {
>>>    	{Opt_min_batch_time, 0, MOPT_GTE0},
>>>    	{Opt_inode_readahead_blks, 0, MOPT_GTE0},
>>>    	{Opt_init_itable, 0, MOPT_GTE0},
>>> -	{Opt_dax, EXT4_MOUNT_DAX_ALWAYS, MOPT_SET},
>>> +	{Opt_dax, EXT4_MOUNT_DAX_ALWAYS, MOPT_SET | MOPT_SKIP},
>>> +	{Opt_dax_always, EXT4_MOUNT_DAX_ALWAYS,
>>> +		MOPT_EXT4_ONLY | MOPT_SET | MOPT_SKIP},
>>> +	{Opt_dax_inode, EXT4_MOUNT2_DAX_INODE,
>>> +		MOPT_EXT4_ONLY | MOPT_SET | MOPT_SKIP},
>>> +	{Opt_dax_never, EXT4_MOUNT2_DAX_NEVER,
>>> +		MOPT_EXT4_ONLY | MOPT_SET | MOPT_SKIP},
>>>    	{Opt_stripe, 0, MOPT_GTE0},
>>>    	{Opt_resuid, 0, MOPT_GTE0},
>>>    	{Opt_resgid, 0, MOPT_GTE0},
>>> @@ -2084,13 +2095,32 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
>>>    		}
>>>    		sbi->s_jquota_fmt = m->mount_opt;
>>>    #endif
>>> -	} else if (token == Opt_dax) {
>>> +	} else if (token == Opt_dax || token == Opt_dax_always ||
>>> +		   token == Opt_dax_inode || token == Opt_dax_never) {
>>>    #ifdef CONFIG_FS_DAX
>>> -		ext4_msg(sb, KERN_WARNING,
>>> -		"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
>>> -		sbi->s_mount_opt |= m->mount_opt;
>>> +		switch (token) {
>>> +		case Opt_dax:
>>> +		case Opt_dax_always:
>>> +			ext4_msg(sb, KERN_WARNING,
>>> +				"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
>>> +			sbi->s_mount_opt |= EXT4_MOUNT_DAX_ALWAYS;
>>> +			sbi->s_mount_opt2&= ~EXT4_MOUNT2_DAX_NEVER;
>>> +			break;
>>> +		case Opt_dax_never:
>>> +			sbi->s_mount_opt2 |= EXT4_MOUNT2_DAX_NEVER;
>>> +			sbi->s_mount_opt&= ~EXT4_MOUNT_DAX_ALWAYS;
>>> +			break;
>>> +		case Opt_dax_inode:
>>> +			sbi->s_mount_opt&= ~EXT4_MOUNT_DAX_ALWAYS;
>>> +			sbi->s_mount_opt2&= ~EXT4_MOUNT2_DAX_NEVER;
>>> +			/* Strictly for printing options */
>>> +			sbi->s_mount_opt2 |= EXT4_MOUNT2_DAX_INODE;
>>> +			break;
>>> +		}
>>>    #else
>>>    		ext4_msg(sb, KERN_INFO, "dax option not supported");
>>> +		sbi->s_mount_opt2 |= EXT4_MOUNT2_DAX_NEVER;
>>> +		sbi->s_mount_opt&= ~EXT4_MOUNT_DAX_ALWAYS;
>>>    		return -1;
>>>    #endif
>>
>> For s_mount_opt/s_mount_opt2, could we make the code more readable by
>> using set_opt()/set_opt2()/clear_opt()/clear_opt2() macros?
>
> I could but it seems like there is a mixture of styles in that function/file...
>
> For me it is really a toss up which is more readable.  I'm inclined to keep it
> since it's been reviewed multiple times.  I was about to send V5 but I'll hold
> off a bit.  If you feel strongly about it I can change it.

It is fine for me to keep it.
I think we can send a separate patch to use unified style in future.

Best Regards,
Xiao Yang
>
> Thanks for the review!
> Ira
>
>>
>> Thanks,
>> Xiao Yang
>>>    	} else if (token == Opt_data_err_abort) {
>>> @@ -2254,7 +2284,7 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
>>>    	for (m = ext4_mount_opts; m->token != Opt_err; m++) {
>>>    		int want_set = m->flags&   MOPT_SET;
>>>    		if (((m->flags&   (MOPT_SET|MOPT_CLEAR)) == 0) ||
>>> -		    (m->flags&   MOPT_CLEAR_ERR))
>>> +		    (m->flags&   MOPT_CLEAR_ERR) || m->flags&   MOPT_SKIP)
>>>    			continue;
>>>    		if (!nodefs&&   !(m->mount_opt&   (sbi->s_mount_opt ^ def_mount_opt)))
>>>    			continue; /* skip if same as the default */
>>> @@ -2314,6 +2344,17 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
>>>    	if (DUMMY_ENCRYPTION_ENABLED(sbi))
>>>    		SEQ_OPTS_PUTS("test_dummy_encryption");
>>>
>>> +	if (test_opt(sb, DAX_ALWAYS)) {
>>> +		if (IS_EXT2_SB(sb))
>>> +			SEQ_OPTS_PUTS("dax");
>>> +		else
>>> +			SEQ_OPTS_PUTS("dax=always");
>>> +	} else if (test_opt2(sb, DAX_NEVER)) {
>>> +		SEQ_OPTS_PUTS("dax=never");
>>> +	} else if (test_opt2(sb, DAX_INODE)) {
>>> +		SEQ_OPTS_PUTS("dax=inode");
>>> +	}
>>> +
>>>    	ext4_show_quota_options(seq, sb);
>>>    	return 0;
>>>    }
>>> @@ -5436,10 +5477,16 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
>>>    		goto restore_opts;
>>>    	}
>>>
>>> -	if ((sbi->s_mount_opt ^ old_opts.s_mount_opt)&   EXT4_MOUNT_DAX_ALWAYS) {
>>> +	if ((sbi->s_mount_opt ^ old_opts.s_mount_opt)&   EXT4_MOUNT_DAX_ALWAYS ||
>>> +	    (sbi->s_mount_opt2 ^ old_opts.s_mount_opt2)&   EXT4_MOUNT2_DAX_NEVER ||
>>> +	    (sbi->s_mount_opt2 ^ old_opts.s_mount_opt2)&   EXT4_MOUNT2_DAX_INODE) {
>>>    		ext4_msg(sb, KERN_WARNING, "warning: refusing change of "
>>> -			"dax flag with busy inodes while remounting");
>>> -		sbi->s_mount_opt ^= EXT4_MOUNT_DAX_ALWAYS;
>>> +			"dax mount option with busy inodes while remounting");
>>> +		sbi->s_mount_opt&= ~EXT4_MOUNT_DAX_ALWAYS;
>>> +		sbi->s_mount_opt |= old_opts.s_mount_opt&   EXT4_MOUNT_DAX_ALWAYS;
>>> +		sbi->s_mount_opt2&= ~(EXT4_MOUNT2_DAX_NEVER | EXT4_MOUNT2_DAX_INODE);
>>> +		sbi->s_mount_opt2 |= old_opts.s_mount_opt2&
>>> +				     (EXT4_MOUNT2_DAX_NEVER | EXT4_MOUNT2_DAX_INODE);
>>>    	}
>>>
>>>    	if (sbi->s_mount_flags&   EXT4_MF_FS_ABORTED)
>>
>>
>>
>
>
> .
>

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