Re: [PATCH v2 04/10] ext4: refactor ext4_zero_range()

[Jan Kara <jack@suse.cz>]

On Wed 04-09-24 14:29:19, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@huawei.com>
> 
> Current ext4_zero_range() is full of complex position calculation and
> stale error out tags. In order to clean up the code and make things
> clear, refactor it by a) simplify and rename variables, b) remove some
> unnecessary position calculations, always write back dirty data and
> drop cache from offset to end, instead of only write back aligned
> blocks, c) rename the stale out_mutex tag.
> 
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/ext4/extents.c | 96 ++++++++++++++++++-----------------------------
>  1 file changed, 37 insertions(+), 59 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index d9fccf2970e9..2fb0c2e303c7 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -4540,40 +4540,15 @@ static long ext4_zero_range(struct file *file, loff_t offset,
>  	struct inode *inode = file_inode(file);
>  	struct address_space *mapping = file->f_mapping;
>  	handle_t *handle = NULL;
> -	unsigned int max_blocks;
>  	loff_t new_size = 0;
> -	int ret = 0;
> -	int flags;
> -	int credits;
> -	int partial_begin, partial_end;
> -	loff_t start, end;
> -	ext4_lblk_t lblk;
> +	loff_t end = offset + len;
> +	ext4_lblk_t start_lblk, end_lblk;
> +	unsigned int blocksize = i_blocksize(inode);
>  	unsigned int blkbits = inode->i_blkbits;
> +	int ret, flags, credits;
>  
>  	trace_ext4_zero_range(inode, offset, len, mode);
>  
> -	/*
> -	 * Round up offset. This is not fallocate, we need to zero out
> -	 * blocks, so convert interior block aligned part of the range to
> -	 * unwritten and possibly manually zero out unaligned parts of the
> -	 * range. Here, start and partial_begin are inclusive, end and
> -	 * partial_end are exclusive.
> -	 */
> -	start = round_up(offset, 1 << blkbits);
> -	end = round_down((offset + len), 1 << blkbits);
> -
> -	if (start < offset || end > offset + len)
> -		return -EINVAL;
> -	partial_begin = offset & ((1 << blkbits) - 1);
> -	partial_end = (offset + len) & ((1 << blkbits) - 1);
> -
> -	lblk = start >> blkbits;
> -	max_blocks = (end >> blkbits);
> -	if (max_blocks < lblk)
> -		max_blocks = 0;
> -	else
> -		max_blocks -= lblk;
> -
>  	inode_lock(inode);
>  
>  	/*
> @@ -4581,26 +4556,23 @@ static long ext4_zero_range(struct file *file, loff_t offset,
>  	 */
>  	if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
>  		ret = -EOPNOTSUPP;
> -		goto out_mutex;
> +		goto out;
>  	}
>  
>  	if (!(mode & FALLOC_FL_KEEP_SIZE) &&
> -	    (offset + len > inode->i_size ||
> -	     offset + len > EXT4_I(inode)->i_disksize)) {
> -		new_size = offset + len;
> +	    (end > inode->i_size || end > EXT4_I(inode)->i_disksize)) {
> +		new_size = end;
>  		ret = inode_newsize_ok(inode, new_size);
>  		if (ret)
> -			goto out_mutex;
> +			goto out;
>  	}
>  
> -	flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT;
> -
>  	/* Wait all existing dio workers, newcomers will block on i_rwsem */
>  	inode_dio_wait(inode);
>  
>  	ret = file_modified(file);
>  	if (ret)
> -		goto out_mutex;
> +		goto out;
>  
>  	/*
>  	 * Prevent page faults from reinstantiating pages we have released
> @@ -4616,36 +4588,40 @@ static long ext4_zero_range(struct file *file, loff_t offset,
>  	 * Write data that will be zeroed to preserve them when successfully
>  	 * discarding page cache below but fail to convert extents.
>  	 */
> -	ret = filemap_write_and_wait_range(mapping, start, end - 1);
> +	ret = filemap_write_and_wait_range(mapping, offset, end - 1);
>  	if (ret)
>  		goto out_invalidate_lock;
>  
> +	/* Now release the pages and zero block aligned part of pages */
> +	truncate_pagecache_range(inode, offset, end - 1);
> +
> +	flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT;
>  	/* Preallocate the range including the unaligned edges */
> -	if (partial_begin || partial_end) {
> -		ret = ext4_alloc_file_blocks(file,
> -				round_down(offset, 1 << blkbits) >> blkbits,
> -				(round_up((offset + len), 1 << blkbits) -
> -				 round_down(offset, 1 << blkbits)) >> blkbits,
> -				new_size, flags);
> +	if (offset & (blocksize - 1) || end & (blocksize - 1)) {
> +		ext4_lblk_t alloc_lblk = offset >> blkbits;
> +		ext4_lblk_t len_lblk = EXT4_MAX_BLOCKS(len, offset, blkbits);
> +
> +		ret = ext4_alloc_file_blocks(file, alloc_lblk, len_lblk,
> +					     new_size, flags);
>  		if (ret)
>  			goto out_invalidate_lock;
>  
>  	}
>  
>  	/* Zero range excluding the unaligned edges */
> -	if (max_blocks > 0) {
> -		flags |= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
> -			  EXT4_EX_NOCACHE);
> -
> -		/* Now release the pages and zero block aligned part of pages */
> -		truncate_pagecache_range(inode, start, end - 1);
> -
> -		ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
> -					     flags);
> +	start_lblk = round_up(offset, blocksize) >> blkbits;
> +	end_lblk = end >> blkbits;
> +	if (end_lblk > start_lblk) {
> +		ext4_lblk_t zero_blks = end_lblk - start_lblk;
> +
> +		flags |= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN | EXT4_EX_NOCACHE);
> +		ret = ext4_alloc_file_blocks(file, start_lblk, zero_blks,
> +					     new_size, flags);
>  		if (ret)
>  			goto out_invalidate_lock;
>  	}
> -	if (!partial_begin && !partial_end)
> +	/* Finish zeroing out if it doesn't contain partial block */
> +	if (!(offset & (blocksize - 1)) && !(end & (blocksize - 1)))
>  		goto out_invalidate_lock;
>  
>  	/*
> @@ -4662,16 +4638,18 @@ static long ext4_zero_range(struct file *file, loff_t offset,
>  		goto out_invalidate_lock;
>  	}
>  
> +	/* Zero out partial block at the edges of the range */
> +	ret = ext4_zero_partial_blocks(handle, inode, offset, len);
> +	if (ret)
> +		goto out_handle;
> +
>  	if (new_size)
>  		ext4_update_inode_size(inode, new_size);
>  	ret = ext4_mark_inode_dirty(handle, inode);
>  	if (unlikely(ret))
>  		goto out_handle;
> -	/* Zero out partial block at the edges of the range */
> -	ret = ext4_zero_partial_blocks(handle, inode, offset, len);
> -	if (ret >= 0)
> -		ext4_update_inode_fsync_trans(handle, inode, 1);
>  
> +	ext4_update_inode_fsync_trans(handle, inode, 1);
>  	if (file->f_flags & O_SYNC)
>  		ext4_handle_sync(handle);
>  
> @@ -4679,7 +4657,7 @@ static long ext4_zero_range(struct file *file, loff_t offset,
>  	ext4_journal_stop(handle);
>  out_invalidate_lock:
>  	filemap_invalidate_unlock(mapping);
> -out_mutex:
> +out:
>  	inode_unlock(inode);
>  	return ret;
>  }
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR