linux-kernel - Re: [PATCH v4 03/10] ext4: don't write back data before punch hole in nojournal mode

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Message-ID: <20241216150222.vrpdnm7ls4bretxl@quack3>
Date: Mon, 16 Dec 2024 16:02:22 +0100
From: Jan Kara <jack@...e.cz>
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,
	chengzhihao1@...wei.com, yukuai3@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH v4 03/10] ext4: don't write back data before punch hole
 in nojournal mode

On Mon 16-12-24 09:39:08, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
> 
> There is no need to write back all data before punching a hole in
> non-journaled mode since it will be dropped soon after removing space.
> Therefore, the call to filemap_write_and_wait_range() can be eliminated.
> Besides, similar to ext4_zero_range(), we must address the case of
> partially punched folios when block size < page size. It is essential to
> remove writable userspace mappings to ensure that the folio can be
> faulted again during subsequent mmap write access.
> 
> In journaled mode, we need to write dirty pages out before discarding
> page cache in case of crash before committing the freeing data
> transaction, which could expose old, stale data, even if synchronization
> has been performed.
> 
> 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 | 18 +++++-------------
>  1 file changed, 5 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index bf735d06b621..a5ba2b71d508 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4018,17 +4018,6 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
>  
>  	trace_ext4_punch_hole(inode, offset, length, 0);
>  
> -	/*
> -	 * Write out all dirty pages to avoid race conditions
> -	 * Then release them.
> -	 */
> -	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
> -		ret = filemap_write_and_wait_range(mapping, offset,
> -						   offset + length - 1);
> -		if (ret)
> -			return ret;
> -	}
> -
>  	inode_lock(inode);
>  
>  	/* No need to punch hole beyond i_size */
> @@ -4090,8 +4079,11 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
>  		ret = ext4_update_disksize_before_punch(inode, offset, length);
>  		if (ret)
>  			goto out_dio;
> -		truncate_pagecache_range(inode, first_block_offset,
> -					 last_block_offset);
> +
> +		ret = ext4_truncate_page_cache_block_range(inode,
> +				first_block_offset, last_block_offset + 1);
> +		if (ret)
> +			goto out_dio;
>  	}
>  
>  	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
> -- 
> 2.46.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR