linux-kernel - Re: [PATCH v2 02/13] ext4: subdivide EXT4_EXT_DATA

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Message-ID: <aSbqoc4qgGf-pp0D@li-dc0c254c-257c-11b2-a85c-98b6c1322444.ibm.com>
Date: Wed, 26 Nov 2025 17:25:13 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
        jack@...e.cz, yi.zhang@...wei.com, yizhang089@...il.com,
        libaokun1@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH v2 02/13] ext4: subdivide EXT4_EXT_DATA_VALID1

On Wed, Nov 26, 2025 at 04:57:27PM +0530, Ojaswin Mujoo wrote:
> On Fri, Nov 21, 2025 at 02:08:00PM +0800, Zhang Yi wrote:
> > From: Zhang Yi <yi.zhang@...wei.com>
> > 
> > When splitting an extent, if the EXT4_GET_BLOCKS_CONVERT flag is set and
> > it is necessary to split the target extent in the middle,
> > ext4_split_extent() first handles splitting the latter half of the
> > extent and passes the EXT4_EXT_DATA_VALID1 flag. This flag implies that
> > all blocks before the split point contain valid data; however, this
> > assumption is incorrect.
> > 
> > Therefore, subdivid EXT4_EXT_DATA_VALID1 into
> > EXT4_EXT_DATA_ENTIRE_VALID1 and EXT4_EXT_DATA_PARTIAL_VALID1, which
> > indicate that the first half of the extent is either entirely valid or
> > only partially valid, respectively. These two flags cannot be set
> > simultaneously.
> > 
> > This patch does not use EXT4_EXT_DATA_PARTIAL_VALID1, it only replaces
> > EXT4_EXT_DATA_VALID1 with EXT4_EXT_DATA_ENTIRE_VALID1 at the location
> > where it is set, no logical changes.
> > 
> > Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> 
> Looks good, feel free to add:
> Reviewed-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> 
> > ---
> >  fs/ext4/extents.c | 18 ++++++++++++------
> >  1 file changed, 12 insertions(+), 6 deletions(-)
> > 
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 91682966597d..f7aa497e5d6c 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -43,8 +43,13 @@
> >  #define EXT4_EXT_MARK_UNWRIT1	0x2  /* mark first half unwritten */
> >  #define EXT4_EXT_MARK_UNWRIT2	0x4  /* mark second half unwritten */
> >  
> > -#define EXT4_EXT_DATA_VALID1	0x8  /* first half contains valid data */
> > -#define EXT4_EXT_DATA_VALID2	0x10 /* second half contains valid data */
> > +/* first half contains valid data */
> > +#define EXT4_EXT_DATA_ENTIRE_VALID1	0x8   /* has partially valid data */
> > +#define EXT4_EXT_DATA_PARTIAL_VALID1	0x10  /* has entirely valid data */

Hey, sorry I forgot to mention this minor typo in my last email. The
comment for partial and entirely valid flags are mismatched :)

Regards,
ojaswin

> > +#define EXT4_EXT_DATA_VALID1		(EXT4_EXT_DATA_ENTIRE_VALID1 | \
> > +					 EXT4_EXT_DATA_PARTIAL_VALID1)
> > +
> > +#define EXT4_EXT_DATA_VALID2	0x20 /* second half contains valid data */
> >  
> >  static __le32 ext4_extent_block_csum(struct inode *inode,
> >  				     struct ext4_extent_header *eh)
> > @@ -3190,8 +3195,9 @@ static struct ext4_ext_path *ext4_split_extent_at(handle_t *handle,
> >  	unsigned int ee_len, depth;
> >  	int err = 0;
> >  
> > -	BUG_ON((split_flag & (EXT4_EXT_DATA_VALID1 | EXT4_EXT_DATA_VALID2)) ==
> > -	       (EXT4_EXT_DATA_VALID1 | EXT4_EXT_DATA_VALID2));
> > +	BUG_ON((split_flag & EXT4_EXT_DATA_VALID1) == EXT4_EXT_DATA_VALID1);
> > +	BUG_ON((split_flag & EXT4_EXT_DATA_VALID1) &&
> > +	       (split_flag & EXT4_EXT_DATA_VALID2));
> >  
> >  	ext_debug(inode, "logical block %llu\n", (unsigned long long)split);
> >  
> > @@ -3358,7 +3364,7 @@ static struct ext4_ext_path *ext4_split_extent(handle_t *handle,
> >  			split_flag1 |= EXT4_EXT_MARK_UNWRIT1 |
> >  				       EXT4_EXT_MARK_UNWRIT2;
> >  		if (split_flag & EXT4_EXT_DATA_VALID2)
> > -			split_flag1 |= EXT4_EXT_DATA_VALID1;
> > +			split_flag1 |= EXT4_EXT_DATA_ENTIRE_VALID1;
> >  		path = ext4_split_extent_at(handle, inode, path,
> >  				map->m_lblk + map->m_len, split_flag1, flags1);
> >  		if (IS_ERR(path))
> > @@ -3717,7 +3723,7 @@ static struct ext4_ext_path *ext4_split_convert_extents(handle_t *handle,
> >  
> >  	/* Convert to unwritten */
> >  	if (flags & EXT4_GET_BLOCKS_CONVERT_UNWRITTEN) {
> > -		split_flag |= EXT4_EXT_DATA_VALID1;
> > +		split_flag |= EXT4_EXT_DATA_ENTIRE_VALID1;
> >  	/* Convert to initialized */
> >  	} else if (flags & EXT4_GET_BLOCKS_CONVERT) {
> >  		split_flag |= ee_block + ee_len <= eof_block ?
> > -- 
> > 2.46.1
> >