linux-ext4 - Re: [PATCH 08/25] ext4: support large block size in ext4

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Message-ID: <kfzwluvt7sb43pl7fr4qexvflentvgm5y2s52kxg4exe6tsq7n@e4kjkexvwtvg>
Date: Mon, 3 Nov 2025 09:27:55 +0100
From: Jan Kara <jack@...e.cz>
To: libaokun@...weicloud.com
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca, 
	jack@...e.cz, linux-kernel@...r.kernel.org, kernel@...kajraghav.com, 
	mcgrof@...nel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	yi.zhang@...wei.com, yangerkun@...wei.com, chengzhihao1@...wei.com, 
	libaokun1@...wei.com
Subject: Re: [PATCH 08/25] ext4: support large block size in ext4_readdir()

On Sat 25-10-25 11:22:04, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
> 
> In ext4_readdir(), page_cache_sync_readahead() is used to readahead mapped
> physical blocks. With LBS support, this can lead to a negative right shift.
> 
> To fix this, the page index is now calculated by first converting the
> physical block number (pblk) to a file position (pos) before converting
> it to a page index. Also, the correct number of pages to readahead is now
> passed.
> 
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> Reviewed-by: Zhang Yi <yi.zhang@...wei.com>

Looks good. Feel free to add:

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

								Honza

> diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
> index d4164c507a90..256fe2c1d4c1 100644
> --- a/fs/ext4/dir.c
> +++ b/fs/ext4/dir.c
> @@ -192,13 +192,13 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
>  			continue;
>  		}
>  		if (err > 0) {
> -			pgoff_t index = map.m_pblk >>
> -					(PAGE_SHIFT - inode->i_blkbits);
> +			pgoff_t index = map.m_pblk << inode->i_blkbits >>
> +					PAGE_SHIFT;
>  			if (!ra_has_index(&file->f_ra, index))
>  				page_cache_sync_readahead(
>  					sb->s_bdev->bd_mapping,
> -					&file->f_ra, file,
> -					index, 1);
> +					&file->f_ra, file, index,
> +					1 << EXT4_SB(sb)->s_min_folio_order);
>  			file->f_ra.prev_pos = (loff_t)index << PAGE_SHIFT;
>  			bh = ext4_bread(NULL, inode, map.m_lblk, 0);
>  			if (IS_ERR(bh)) {
> -- 
> 2.46.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR