linux-ext4 - Re: [PATCH 24/31] ext4: Convert ext4_mpage

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Message-ID: <Y9NPyMThUWG5hxX6@sol.localdomain>
Date:   Thu, 26 Jan 2023 20:15:04 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     Theodore Tso <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 24/31] ext4: Convert ext4_mpage_readpages() to work on
 folios

On Thu, Jan 26, 2023 at 08:24:08PM +0000, Matthew Wilcox (Oracle) wrote:
>  int ext4_mpage_readpages(struct inode *inode,
> -		struct readahead_control *rac, struct page *page)
> +		struct readahead_control *rac, struct folio *folio)
>  {
>  	struct bio *bio = NULL;
>  	sector_t last_block_in_bio = 0;
> @@ -247,16 +247,15 @@ int ext4_mpage_readpages(struct inode *inode,
>  		int fully_mapped = 1;
>  		unsigned first_hole = blocks_per_page;
>  
> -		if (rac) {
> -			page = readahead_page(rac);
> -			prefetchw(&page->flags);
> -		}
> +		if (rac)
> +			folio = readahead_folio(rac);
> +		prefetchw(&folio->flags);

Unlike readahead_page(), readahead_folio() puts the folio immediately.  Is that
really safe?

> @@ -299,11 +298,11 @@ int ext4_mpage_readpages(struct inode *inode,
>  
>  				if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
>  				set_error_page:
> -					SetPageError(page);
> -					zero_user_segment(page, 0,
> -							  PAGE_SIZE);
> -					unlock_page(page);
> -					goto next_page;
> +					folio_set_error(folio);
> +					folio_zero_segment(folio, 0,
> +							  folio_size(folio));
> +					folio_unlock(folio);
> +					continue;

This is 'continuing' the inner loop, not the outer loop as it should.

- Eric