linux-ext4 - Re: [PATCH v2 1/4] ext4: check and update i

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Date:   Thu, 15 Jul 2021 13:52:01 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhang Yi <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, yukuai3@...wei.com
Subject: Re: [PATCH v2 1/4] ext4: check and update i_disksize properly

On Thu 15-07-21 09:54:49, Zhang Yi wrote:
> After commit 3da40c7b0898 ("ext4: only call ext4_truncate when size <=
> isize"), i_disksize could always be updated to i_size in ext4_setattr(),
> and we could sure that i_disksize <= i_size since holding inode lock and
> if i_disksize < i_size there are delalloc writes pending in the range
> upto i_size. If the end of the current write is <= i_size, there's no
> need to touch i_disksize since writeback will push i_disksize upto
> i_size eventually. So we can switch to check i_size instead of
> i_disksize in ext4_da_write_end() when write to the end of the file.
> we also could remove ext4_mark_inode_dirty() together because we defer
> inode dirtying to generic_write_end() or ext4_da_write_inline_data_end().
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>

Looks good. Feel free to add:

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

								Honza

> ---
>  fs/ext4/inode.c | 34 ++++++++++++++++++----------------
>  1 file changed, 18 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index d8de607849df..dca8e3810443 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3084,35 +3084,37 @@ static int ext4_da_write_end(struct file *file,
>  	end = start + copied - 1;
>  
>  	/*
> -	 * generic_write_end() will run mark_inode_dirty() if i_size
> -	 * changes.  So let's piggyback the i_disksize mark_inode_dirty
> -	 * into that.
> +	 * Since we are holding inode lock, we are sure i_disksize <=
> +	 * i_size. We also know that if i_disksize < i_size, there are
> +	 * delalloc writes pending in the range upto i_size. If the end of
> +	 * the current write is <= i_size, there's no need to touch
> +	 * i_disksize since writeback will push i_disksize upto i_size
> +	 * eventually. If the end of the current write is > i_size and
> +	 * inside an allocated block (ext4_da_should_update_i_disksize()
> +	 * check), we need to update i_disksize here as neither
> +	 * ext4_writepage() nor certain ext4_writepages() paths not
> +	 * allocating blocks update i_disksize.
> +	 *
> +	 * Note that we defer inode dirtying to generic_write_end() /
> +	 * ext4_da_write_inline_data_end().
>  	 */
>  	new_i_size = pos + copied;
> -	if (copied && new_i_size > EXT4_I(inode)->i_disksize) {
> +	if (copied && new_i_size > inode->i_size) {
>  		if (ext4_has_inline_data(inode) ||
> -		    ext4_da_should_update_i_disksize(page, end)) {
> +		    ext4_da_should_update_i_disksize(page, end))
>  			ext4_update_i_disksize(inode, new_i_size);
> -			/* We need to mark inode dirty even if
> -			 * new_i_size is less that inode->i_size
> -			 * bu greater than i_disksize.(hint delalloc)
> -			 */
> -			ret = ext4_mark_inode_dirty(handle, inode);
> -		}
>  	}
>  
>  	if (write_mode != CONVERT_INLINE_DATA &&
>  	    ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) &&
>  	    ext4_has_inline_data(inode))
> -		ret2 = ext4_da_write_inline_data_end(inode, pos, len, copied,
> +		ret = ext4_da_write_inline_data_end(inode, pos, len, copied,
>  						     page);
>  	else
> -		ret2 = generic_write_end(file, mapping, pos, len, copied,
> +		ret = generic_write_end(file, mapping, pos, len, copied,
>  							page, fsdata);
>  
> -	copied = ret2;
> -	if (ret2 < 0)
> -		ret = ret2;
> +	copied = ret;
>  	ret2 = ext4_journal_stop(handle);
>  	if (unlikely(ret2 && !ret))
>  		ret = ret2;
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR