Re: [f2fs-dev] [PATCH v2] f2fs: fix has_curseg_enough_space to check all data segments for dentry blocks

[Jaegeuk Kim via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

I need to drop this patch, since this breaks xfstests such as f2fs/005.

Please revisit the issue.

On 11/11, 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 merging the dentry block check into the main data/node block
> check loop and checking data_blocks + dent_blocks for data segments,
> since both regular data blocks and dentry blocks can be written to the
> same segment. When active_logs == 6, dentry blocks can be allocated to
> any of the three data segments (HOT, WARM, COLD), so all three segments
> need to account for dentry blocks. When active_logs != 6, dentry blocks
> are always allocated to HOT_DATA segment only, so only HOT_DATA segment
> needs to account for dentry blocks, while WARM and COLD segments only
> check data_blocks.
> 
> Fixes: ef095d19e82f ("f2fs: write small sized IO to hot log")
> Cc: stable@kernel.org
> Signed-off-by: Xiaole He <hexiaole1994@126.com>
> ---
> Changes in v2 (per Yongpeng's feedback):
> - Merged dentry block check into the main loop to avoid duplication
> - Check data_blocks + dent_blocks for data segments (both can write to same segment)
> ---
>  fs/f2fs/segment.h | 24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index 1ce2c8abaf48..acda720a54eb 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -626,21 +626,21 @@ static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi,
>  
>  		left_blocks = get_left_section_blocks(sbi, i, segno);
>  
> -		blocks = i <= CURSEG_COLD_DATA ? data_blocks : node_blocks;
> +		if (i <= CURSEG_COLD_DATA) {
> +			blocks = data_blocks;
> +			/*
> +			 * With active_logs == 6, dentry blocks can be allocated to
> +			 * any data segment. With active_logs != 6, dentry blocks
> +			 * are always allocated to HOT_DATA segment.
> +			 */
> +			if ((F2FS_OPTION(sbi).active_logs == 6) || (i == CURSEG_HOT_DATA))
> +				blocks += dent_blocks;
> +		} else {
> +			blocks = node_blocks;
> +		}
>  		if (blocks > left_blocks)
>  			return false;
>  	}
> -
> -	/* check current data section for dentry blocks. */
> -	segno = CURSEG_I(sbi, CURSEG_HOT_DATA)->segno;
> -
> -	if (unlikely(segno == NULL_SEGNO))
> -		return false;
> -
> -	left_blocks = get_left_section_blocks(sbi, CURSEG_HOT_DATA, segno);
> -
> -	if (dent_blocks > left_blocks)
> -		return false;
>  	return true;
>  }
>  
> -- 
> 2.43.0


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