linux-kernel - Re: [PATCH v1 3/5] f2fs: add f2fs_block_needs

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Message-ID: <9b4f9818-f8fd-4af2-8f5e-bab768bac8c9@kernel.org>
Date: Tue, 6 Jan 2026 17:19:14 +0800
From: Chao Yu <chao@...nel.org>
To: Nanzhe Zhao <nzzhao@....com>, Kim Jaegeuk <jaegeuk@...nel.org>
Cc: chao@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/5] f2fs: add f2fs_block_needs_zeroing() to handle
 hole blocks

On 1/5/2026 11:30 PM, Nanzhe Zhao wrote:
> f2fs_read_data_large_folio() relies on f2fs_map_blocks() to decide whether
> a subpage should be zero-filled or queued to a read bio.
> 
> However, f2fs_map_blocks() can set F2FS_MAP_MAPPED for NULL_ADDR and
> NEW_ADDR in the non-DIO, no-create path. The large folio read code then

Nanzhe,

IIUC, f2fs_map_blocks(inode, &map, F2FS_GET_BLOCK_DEFAULT) won't map hole
space, or am I missing something?

Thanks,

> treats such hole blocks as mapped blocks, and may account them
> in read_pages_pending and attempt to build bios for them, which can
> leave tasks stuck in readahead for heavily fragmented files.
> 
> Add a helper, f2fs_block_needs_zeroing(), which detects NULL_ADDR and
> NEW_ADDR from struct f2fs_map_blocks. Use it to prioritize the zeroing
> path by checking f2fs_block_needs_zeroing() before
> (map.m_flags & F2FS_MAP_MAPPED) under got_it: label.
> 
> Signed-off-by: Nanzhe Zhao <nzzhao@....com>
> ---
>   fs/f2fs/data.c | 21 +++++++++++++--------
>   1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 4bef04560924..66ab7a43a56f 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2413,6 +2413,11 @@ static void ffs_detach_free(struct folio *folio)
>   	kmem_cache_free(ffs_entry_slab, ffs);
>   }
> 
> +static inline bool f2fs_block_needs_zeroing(const struct f2fs_map_blocks *map)
> +{
> +	return map->m_pblk == NULL_ADDR || map->m_pblk == NEW_ADDR;
> +}
> +
>   static int f2fs_read_data_large_folio(struct inode *inode,
>   		struct readahead_control *rac, struct folio *folio)
>   {
> @@ -2468,14 +2473,7 @@ static int f2fs_read_data_large_folio(struct inode *inode,
>   		if (ret)
>   			goto err_out;
>   got_it:
> -		if ((map.m_flags & F2FS_MAP_MAPPED)) {
> -			block_nr = map.m_pblk + index - map.m_lblk;
> -			if (!f2fs_is_valid_blkaddr(F2FS_I_SB(inode), block_nr,
> -						DATA_GENERIC_ENHANCE_READ)) {
> -				ret = -EFSCORRUPTED;
> -				goto err_out;
> -			}
> -		} else {
> +		if ((f2fs_block_needs_zeroing(&map))) {
>   			folio_zero_range(folio, offset << PAGE_SHIFT, PAGE_SIZE);
>   			if (f2fs_need_verity(inode, index) &&
>   			    !fsverity_verify_page(folio_file_page(folio,
> @@ -2484,6 +2482,13 @@ static int f2fs_read_data_large_folio(struct inode *inode,
>   				goto err_out;
>   			}
>   			continue;
> +		} else if((map.m_flags & F2FS_MAP_MAPPED)) {
> +			block_nr = map.m_pblk + index - map.m_lblk;
> +			if (!f2fs_is_valid_blkaddr(F2FS_I_SB(inode), block_nr,
> +						DATA_GENERIC_ENHANCE_READ)) {
> +				ret = -EFSCORRUPTED;
> +				goto err_out;
> +			}
>   		}
> 
>   		/* We must increment read_pages_pending before possible BIOs submitting
> --
> 2.34.1
>