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Message-ID: <aS8pQtLGoigY25hi@google.com>
Date: Tue, 2 Dec 2025 18:00:34 +0000
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Xiaole He <hexiaole1994@....com>
Cc: linux-f2fs-devel@...ts.sourceforge.net, chao@...nel.org,
linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH v2] f2fs: fix has_curseg_enough_space to check all data
segments for dentry blocks
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@...nel.org
> Signed-off-by: Xiaole He <hexiaole1994@....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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