Re: [f2fs-dev] [PATCH] f2fs: avoid f2fs_map_blocks() for consecutive holes in readpages

[Nanzhe Zhao <nzzhao@126.com>]

Hi Chao:

On 2026/1/12 09:33, Chao Yu via Linux-f2fs-devel wrote:
> For consecutive large hole mapping across {d,id,did}nodes , we don't
> need to call f2fs_map_blocks() to check one hole block per one time,
> instead, we can use map.m_next_pgofs as a hint of next potential valid
> block, so that we can skip calling f2fs_map_blocks the range of
> [cur_pgofs + 1, .m_next_pgofs).
> 
> 1) regular case
> 
> touch /mnt/f2fs/file
> truncate -s $((1024*1024*1024)) /mnt/f2fs/file
> time dd if=/mnt/f2fs/file of=/dev/null bs=1M count=1024
> 
> Before:
> real    0m0.706s
> user    0m0.000s
> sys     0m0.706s
> 
> After:
> real    0m0.620s
> user    0m0.008s
> sys     0m0.611s
> 
> 2) large folio case
> 
> touch /mnt/f2fs/file
> truncate -s $((1024*1024*1024)) /mnt/f2fs/file
> f2fs_io setflags immutable /mnt/f2fs/file
> sync
> echo 3 > /proc/sys/vm/drop_caches
> time dd if=/mnt/f2fs/file of=/dev/null bs=1M count=1024
> 
> Before:
> real    0m0.438s
> user    0m0.004s
> sys     0m0.433s
> 
> After:
> real    0m0.368s
> user    0m0.004s
> sys     0m0.364s
> 
> Signed-off-by: Chao Yu <chao@kernel.org>
> ---
>   fs/f2fs/data.c | 21 +++++++++++++++------
>   1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index a2c4769d0ae1..5b0642cd27ff 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2176,10 +2176,13 @@ static int f2fs_read_single_page(struct inode *inode, struct folio *folio,
>   	/*
>   	 * Map blocks using the previous result first.
>   	 */
> -	if ((map->m_flags & F2FS_MAP_MAPPED) &&
> -			block_in_file > map->m_lblk &&
> +	if (map->m_flags & F2FS_MAP_MAPPED) {
> +		if (block_in_file > map->m_lblk &&
>   			block_in_file < (map->m_lblk + map->m_len))
> +			goto got_it;
> +	} else if (block_in_file < *map->m_next_pgofs) {
>   		goto got_it;
> +	}
>   
>   	/*
>   	 * Then do more f2fs_map_blocks() calls until we are
> @@ -2454,7 +2457,7 @@ static int f2fs_read_data_large_folio(struct inode *inode,
>   	struct bio *bio = NULL;
>   	sector_t last_block_in_bio = 0;
>   	struct f2fs_map_blocks map = {0, };
> -	pgoff_t index, offset;
> +	pgoff_t index, offset, next_pgofs = 0;
>   	unsigned max_nr_pages = rac ? readahead_count(rac) :
>   				folio_nr_pages(folio);
>   	unsigned nrpages;
> @@ -2487,16 +2490,21 @@ static int f2fs_read_data_large_folio(struct inode *inode,
>   		/*
>   		 * Map blocks using the previous result first.
>   		 */
> -		if ((map.m_flags & F2FS_MAP_MAPPED) &&
> -				index > map.m_lblk &&
> +		if (map.m_flags & F2FS_MAP_MAPPED) {
> +			if (index > map.m_lblk &&
>   				index < (map.m_lblk + map.m_len))
> +				goto got_it;
> +		} else if (index < next_pgofs) {
> +			/* hole case */
>   			goto got_it;
> +		}
>   
>   		/*
>   		 * Then do more f2fs_map_blocks() calls until we are
>   		 * done with this page.
>   		 */
>   		memset(&map, 0, sizeof(map));
> +		map.m_next_pgofs = &next_pgofs;
>   		map.m_seg_type = NO_CHECK_TYPE;
>   		map.m_lblk = index;
>   		map.m_len = max_nr_pages;
> @@ -2617,6 +2625,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
>   	pgoff_t nc_cluster_idx = NULL_CLUSTER;
>   	pgoff_t index;
>   #endif
> +	pgoff_t next_pgofs = 0;
>   	unsigned nr_pages = rac ? readahead_count(rac) : 1;
>   	struct address_space *mapping = rac ? rac->mapping : folio->mapping;
>   	unsigned max_nr_pages = nr_pages;
> @@ -2637,7 +2646,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
>   	map.m_lblk = 0;
>   	map.m_len = 0;
>   	map.m_flags = 0;
> -	map.m_next_pgofs = NULL;
> +	map.m_next_pgofs = &next_pgofs;
>   	map.m_next_extent = NULL;
>   	map.m_seg_type = NO_CHECK_TYPE;
>   	map.m_may_create = false;

Do we have plans to also support reducing f2fs_map_blocks() calls for 
consectives holes in logical file postion with dnode have already been
allocated in buffered large folio read?
Such as consective NULL_ADDR or NEW_ADDR?

Thanks,