linux-kernel - Re: [PATCH 13/17] writeback: Factor writeback_get_folio() out of write_cache

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Date: Thu, 21 Dec 2023 12:41:53 +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 13/17] writeback: Factor writeback_get_folio() out of
 write_cache_pages()

On Mon 18-12-23 16:35:49, Christoph Hellwig wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> Move the loop for should-we-write-this-folio to its own function.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Signed-off-by: Christoph Hellwig <hch@....de>

Looks good to me. Feel free to add:

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

But I'd note that the call stack depth of similarly called helper functions
(with more to come later in the series) is getting a bit confusing. Maybe
we should inline writeback_get_next() into its single caller
writeback_get_folio() to reduce confusion a bit...

								Honza

> +static struct folio *writeback_get_folio(struct address_space *mapping,
> +		struct writeback_control *wbc)
> +{
> +	struct folio *folio;
> +
> +	for (;;) {
> +		folio = writeback_get_next(mapping, wbc);
> +		if (!folio)
> +			return NULL;
> +		folio_lock(folio);
> +		if (likely(should_writeback_folio(mapping, wbc, folio)))
> +			break;
> +		folio_unlock(folio);
> +	}
> +
> +	trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
> +	return folio;
> +}
> +
>  static struct folio *writeback_iter_init(struct address_space *mapping,
>  		struct writeback_control *wbc)
>  {
> @@ -2455,7 +2474,7 @@ static struct folio *writeback_iter_init(struct address_space *mapping,
>  
>  	wbc->err = 0;
>  	folio_batch_init(&wbc->fbatch);
> -	return writeback_get_next(mapping, wbc);
> +	return writeback_get_folio(mapping, wbc);
>  }
>  
>  /**
> @@ -2498,17 +2517,9 @@ int write_cache_pages(struct address_space *mapping,
>  
>  	for (folio = writeback_iter_init(mapping, wbc);
>  	     folio;
> -	     folio = writeback_get_next(mapping, wbc)) {
> +	     folio = writeback_get_folio(mapping, wbc)) {
>  		unsigned long nr;
>  
> -		folio_lock(folio);
> -		if (!should_writeback_folio(mapping, wbc, folio)) {
> -			folio_unlock(folio);
> -			continue;
> -		}
> -
> -		trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
> -
>  		error = writepage(folio, wbc, data);
>  		nr = folio_nr_pages(folio);
>  		wbc->nr_to_write -= nr;
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR