linux-ext4 - Re: [PATCH] ext4: use writeback_iter in ext4_journalled_submit_inode_data

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Message-ID: <f35c4ecd-48ca-4f41-8457-4b5bfc1e83b8@huaweicloud.com>
Date: Thu, 8 May 2025 10:48:44 +0800
From: Zhang Yi <yi.zhang@...weicloud.com>
To: Christoph Hellwig <hch@....de>
Cc: adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH] ext4: use writeback_iter in
 ext4_journalled_submit_inode_data_buffers

On 2025/5/5 17:16, Christoph Hellwig wrote:
> Use writeback_iter directly instead of write_cache_pages for a nicer
> code structure and less indirect calls.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>

It looks clearer now.

Reviewed-by: Zhang Yi <yi.zhang@...wei.com>

> ---
>  fs/ext4/super.c | 46 ++++++++++++++++++++++------------------------
>  1 file changed, 22 insertions(+), 24 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 181934499624..6a0a3493ee43 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -508,21 +508,9 @@ static void ext4_journal_commit_callback(journal_t *journal, transaction_t *txn)
>  	ext4_maybe_update_superblock(sb);
>  }
>  
> -/*
> - * This writepage callback for write_cache_pages()
> - * takes care of a few cases after page cleaning.
> - *
> - * write_cache_pages() already checks for dirty pages
> - * and calls clear_page_dirty_for_io(), which we want,
> - * to write protect the pages.
> - *
> - * However, we may have to redirty a page (see below.)
> - */
> -static int ext4_journalled_writepage_callback(struct folio *folio,
> -					      struct writeback_control *wbc,
> -					      void *data)
> +static bool ext4_journalled_writepage_needs_redirty(struct jbd2_inode *jinode,
> +		struct folio *folio)
>  {
> -	transaction_t *transaction = (transaction_t *) data;
>  	struct buffer_head *bh, *head;
>  	struct journal_head *jh;
>  
> @@ -543,15 +531,12 @@ static int ext4_journalled_writepage_callback(struct folio *folio,
>  		 */
>  		jh = bh2jh(bh);
>  		if (buffer_dirty(bh) ||
> -		    (jh && (jh->b_transaction != transaction ||
> -			    jh->b_next_transaction))) {
> -			folio_redirty_for_writepage(wbc, folio);
> -			goto out;
> -		}
> +		    (jh && (jh->b_transaction != jinode->i_transaction ||
> +			    jh->b_next_transaction)))
> +			return true;
>  	} while ((bh = bh->b_this_page) != head);
>  
> -out:
> -	return AOP_WRITEPAGE_ACTIVATE;
> +	return false;
>  }
>  
>  static int ext4_journalled_submit_inode_data_buffers(struct jbd2_inode *jinode)
> @@ -563,10 +548,23 @@ static int ext4_journalled_submit_inode_data_buffers(struct jbd2_inode *jinode)
>  		.range_start = jinode->i_dirty_start,
>  		.range_end = jinode->i_dirty_end,
>          };
> +	struct folio *folio = NULL;
> +	int error;
>  
> -	return write_cache_pages(mapping, &wbc,
> -				 ext4_journalled_writepage_callback,
> -				 jinode->i_transaction);
> +	/*
> +	 * writeback_iter() already checks for dirty pages and calls
> +	 * folio_clear_dirty_for_io(), which we want to write protect the
> +	 * folios.
> +	 *
> +	 * However, we may have to redirty a folio sometimes.
> +	 */
> +	while ((folio = writeback_iter(mapping, &wbc, folio, &error))) {
> +		if (ext4_journalled_writepage_needs_redirty(jinode, folio))
> +			folio_redirty_for_writepage(&wbc, folio);
> +		folio_unlock(folio);
> +	}
> +
> +	return error;
>  }
>  
>  static int ext4_journal_submit_inode_data_buffers(struct jbd2_inode *jinode)