linux-kernel - Re: [PATCH 15/17] writeback: Add for_each_writeback

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Date: Thu, 21 Dec 2023 12:51:49 +0100
From: Jan Kara <jack@...e.cz>
To: Christoph Hellwig <hch@....de>
Cc: linux-mm@...ck.org, "Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Jan Kara <jack@...e.com>, David Howells <dhowells@...hat.com>,
	Brian Foster <bfoster@...hat.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/17] writeback: Add for_each_writeback_folio()

On Mon 18-12-23 16:35:51, Christoph Hellwig wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> Wrap up the iterator with a nice bit of syntactic sugar.  Now the
> caller doesn't need to know about wbc->err and can just return error,
> not knowing that the iterator took care of storing errors correctly.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Signed-off-by: Christoph Hellwig <hch@....de>

Not sure if the trick with 'error' variable isn't a bit too clever for us
;) We'll see how many bugs it will cause in the future... Feel free to add:

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

								Honza


> +#define for_each_writeback_folio(mapping, wbc, folio, error)		\
> +	for (folio = writeback_iter_init(mapping, wbc);			\
> +	     folio || ((error = wbc->err), false);			\
> +	     folio = writeback_iter_next(mapping, wbc, folio, error))
> +
>  typedef int (*writepage_t)(struct folio *folio, struct writeback_control *wbc,
>  				void *data);
>  
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 0771f19950081f..fbffd30a9cc93f 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2463,7 +2463,7 @@ static struct folio *writeback_get_folio(struct address_space *mapping,
>  	return folio;
>  }
>  
> -static struct folio *writeback_iter_init(struct address_space *mapping,
> +struct folio *writeback_iter_init(struct address_space *mapping,
>  		struct writeback_control *wbc)
>  {
>  	if (wbc->range_cyclic)
> @@ -2479,7 +2479,7 @@ static struct folio *writeback_iter_init(struct address_space *mapping,
>  	return writeback_get_folio(mapping, wbc);
>  }
>  
> -static struct folio *writeback_iter_next(struct address_space *mapping,
> +struct folio *writeback_iter_next(struct address_space *mapping,
>  		struct writeback_control *wbc, struct folio *folio, int error)
>  {
>  	unsigned long nr = folio_nr_pages(folio);
> @@ -2557,9 +2557,7 @@ int write_cache_pages(struct address_space *mapping,
>  	struct folio *folio;
>  	int error;
>  
> -	for (folio = writeback_iter_init(mapping, wbc);
> -	     folio;
> -	     folio = writeback_iter_next(mapping, wbc, folio, error))
> +	for_each_writeback_folio(mapping, wbc, folio, error)
>  		error = writepage(folio, wbc, data);
>  
>  	return wbc->err;
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR