Re: [PATCH v2 08/24] ext4: support large block size in ext4_readdir()

[Pankaj Raghav]

On 11/7/25 15:42, libaokun@xxxxxxxxxxxxxxx wrote:
> From: Baokun Li <libaokun1@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> Reviewed-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
> Reviewed-by: Jan Kara <jack@xxxxxxx>
> ---
Minor general comments below.

Reviewed-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>

>  fs/ext4/dir.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> 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;

It will be nice to have some common helper for this operation. We do something
similar in filemap.c as well.

>  			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);
Just a personal opinion but it would be nice to have some variable for this instead of doing it
inline? It could be defined along with index.

unsigned long min_nr_pages = 1UL << 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)) {