Re: [f2fs-dev] [PATCH v1] f2fs: fix has_curseg_enough_space to check all data segments for dentry blocks

[Yongpeng Yang <yangyongpeng.storage@gmail.com>]

On 11/10/25 21:26, Xiaole He wrote:
> When active_logs == 6, dentry blocks can be allocated to HOT, WARM, or
> COLD segments based on various conditions in __get_segment_type_6():
> - age extent cache (if enabled)
> - FI_HOT_DATA flag (set when dirty_pages <= min_hot_blocks)
> - rw_hint (defaults to WARM via f2fs_rw_hint_to_seg_type)
> - file_is_hot(), FI_NEED_IPU, f2fs_is_cow_file(), etc.
> 
> However, has_curseg_enough_space() only checked CURSEG_HOT_DATA segment
> for dentry blocks, which could lead to incorrect space calculation when
> dentry blocks are actually allocated to WARM or COLD segments.
> 
> Reproducer:
> Note: This reproducer requires adding a tracepoint to observe segment
> type. Add the following tracepoint to include/trace/events/f2fs.h:
> 
> TRACE_EVENT(f2fs_allocate_data_block,
>          TP_PROTO(struct f2fs_sb_info *sbi, struct inode *inode,
>                  enum log_type type, block_t blkaddr),
> 
>          TP_ARGS(sbi, inode, type, blkaddr),
> 
>          TP_STRUCT__entry(
>                  __field(dev_t, dev)
>                  __field(ino_t, ino)
>                  __field(int, type)
>                  __field(block_t, blkaddr)
>                  __field(int, is_dir)
>          ),
> 
>          TP_fast_assign(
>                  __entry->dev = sbi->sb->s_dev;
>                  __entry->ino = inode ? inode->i_ino : 0;
>                  __entry->type = type;
>                  __entry->blkaddr = blkaddr;
>                  __entry->is_dir = inode ? S_ISDIR(inode->i_mode) : 0;
>          ),
> 
>          TP_printk("dev = (%d,%d), ino = %lu, %s, blkaddr = %u, is_dir = %d",
>                  show_dev(__entry->dev),
>                  (unsigned long)__entry->ino,
>                  show_data_type(__entry->type),
>                  __entry->blkaddr,
>                  __entry->is_dir)
> );
> 
> And add the tracepoint call in fs/f2fs/segment.c in
> f2fs_allocate_data_block() function. Find the location after
> locate_dirty_segment() calls and before IS_DATASEG() check:
> 
> 	locate_dirty_segment(sbi, GET_SEGNO(sbi, old_blkaddr));
> 	locate_dirty_segment(sbi, GET_SEGNO(sbi, *new_blkaddr));
> 
> 	trace_f2fs_allocate_data_block(sbi, folio ? folio->mapping->host : NULL,
> 					type, *new_blkaddr);
> 
> 	if (IS_DATASEG(curseg->seg_type))
> 
> 1. Mount F2FS with active_logs=6 and age extent cache disabled:
>     # mkfs.f2fs -f /dev/sdb1
>     # mount -t f2fs -o active_logs=6 /dev/sdb1 /mnt/f2fs-test
> 
> 2. Enable tracing and f2fs_allocate_data_block tracepoint:
>     # echo 1 > /sys/kernel/debug/tracing/events/f2fs/f2fs_allocate_data_block/enable
>     # echo 1 > /sys/kernel/debug/tracing/tracing_on
>     # echo > /sys/kernel/debug/tracing/trace
> 
> 3. Create a directory and write enough files to trigger dirty_pages >
>     min_hot_blocks (default 16), which will clear FI_HOT_DATA flag:
>     # mkdir /mnt/f2fs-test/testdir
>     # cd /mnt/f2fs-test/testdir
>     # seq 1 8192 | xargs touch
>     # sync
> 
> 4. Observe dentry block allocation:
>     # cat /sys/kernel/debug/tracing/trace
> 
>     The trace output shows dentry blocks (is_dir = 1) allocated to WARM
>     segment because FI_HOT_DATA is cleared when dirty_pages >
>     min_hot_blocks (default 16). However, has_curseg_enough_space() only
>     checked HOT_DATA segment space.
> 
> Fix by checking all three data segments (HOT, WARM, COLD) when
> active_logs == 6, similar to how __get_segment_type_6() can return
> any of these segment types for dentry blocks.
> 
> Fixes: ef095d19e82f ("f2fs: write small sized IO to hot log")
> Cc: stable@kernel.org
> Signed-off-by: Xiaole He <hexiaole1994@126.com>
> ---
>   fs/f2fs/segment.h | 31 +++++++++++++++++++++++++------
>   1 file changed, 25 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index 1ce2c8abaf48..c13400a53013 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -632,15 +632,34 @@ static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi,
>   	}
>   
>   	/* check current data section for dentry blocks. */
> -	segno = CURSEG_I(sbi, CURSEG_HOT_DATA)->segno;
> +	if (F2FS_OPTION(sbi).active_logs == 6) {
> +		/*
> +		 * With active_logs == 6, dentry blocks can be allocated to
> +		 * HOT, WARM, or COLD segments based on age extent cache,
> +		 * FI_HOT_DATA flag, rw_hint, etc. Check all three.
> +		 */
> +		for (i = CURSEG_HOT_DATA; i <= CURSEG_COLD_DATA; i++) {
> +			segno = CURSEG_I(sbi, i)->segno;
> +
> +			if (unlikely(segno == NULL_SEGNO))
> +				return false;
> +
> +			left_blocks = get_left_section_blocks(sbi, i, segno);
> +
> +			if (dent_blocks > left_blocks)
> +				return false;
> +		}

How about merging this for-loop with the one above to avoid duplicated
code? Since both dent_blocks and data_blocks may write to data segments,
should we also check whether data_blocks + dent_blocks > left_blocks?

Yongpeng,


> +	} else {
> +		segno = CURSEG_I(sbi, CURSEG_HOT_DATA)->segno;
>   
> -	if (unlikely(segno == NULL_SEGNO))
> -		return false;
> +		if (unlikely(segno == NULL_SEGNO))
> +			return false;
>   
> -	left_blocks = get_left_section_blocks(sbi, CURSEG_HOT_DATA, segno);
> +		left_blocks = get_left_section_blocks(sbi, CURSEG_HOT_DATA, segno);
>   
> -	if (dent_blocks > left_blocks)
> -		return false;
> +		if (dent_blocks > left_blocks)
> +			return false;
> +	}
>   	return true;
>   }
>