Re: [PATCH] f2fs: fix to round down start offset of fallocate for pin file

[Chao Yu]

On 6/22/26 10:38, Sunmin Jeong wrote:
> Currently, the length of fallocate for pin file is section-aligned to
> keep allocated sections from being selected as victims of GC. However,
> for the case that the start offset of fallocate is not aligned in
> section, the allocated sections can't be fully utilized. It's because a
> new section is allocated by f2fs_allocate_pinning_section() after using
> blks_per_sec blocks regardless of the start offset. As a result, several
> unexpected dirty segments may be created, including blocks assigned to
> the pinned file.
>
> To address this issue, let's round down the start offset of fallocate
> to the length of section.

It's good catch!

> The reproducing scenario is as below
>
> chunk=$(((2<<20)+4096)) # 2MB + 4KB
> touch test
> f2fs_io pinfile set test
> f2fs_io fallocate 0 0 $chunk test
> f2fs_io fallocate 0 $chunk $chunk test
> f2fs_io fallocate 0 $((chunk*2)) $chunk test
> f2fs_io fiemap 0 $((chunk*3)) test
>
> Fiemap: offset = 0 len = 12288
>      logical addr.    physical addr.   length           flags
> 0   0000000000000000 000000068c600000 0000000000400000 00001088
> 1   0000000000400000 000000003d400000 0000000000001000 00001088
> 2   0000000000401000 00000003eb200000 0000000000200000 00001088
> 3   0000000000601000 00000005e4200000 0000000000001000 00001088
> 4   0000000000602000 0000000605400000 0000000000200000 00001089

Fixes and Cc stable line.

> Reviewed-by: Yunji Kang <yunji0.kang@xxxxxxxxxxx>
> Reviewed-by: Yeongjin Gil <youngjin.gil@xxxxxxxxxxx>
> Reviewed-by: Sungjong Seo <sj1557.seo@xxxxxxxxxxx>
> Signed-off-by: Sunmin Jeong <s_min.jeong@xxxxxxxxxxx>
> ---
>   fs/f2fs/file.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 2c4880f24b54..3954aea43bd9 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1906,8 +1906,13 @@ static int f2fs_expand_inode_data(struct inode *inode, loff_t offset,
>   
>   	if (f2fs_is_pinned_file(inode)) {
>   		block_t sec_blks = CAP_BLKS_PER_SEC(sbi);
> -		block_t sec_len = roundup(map.m_len, sec_blks);
> +		block_t sec_len;
>   
> +		if (map.m_lblk % sec_blks) {
> +			map.m_lblk = rounddown(map.m_lblk, sec_blks);
> +			map.m_len = pg_end - map.m_lblk;

If pg_end is aligned to sec_blks, but off_end is non-zero, is there off-by-one issue?

Thanks,

> +		}
> +		sec_len = roundup(map.m_len, sec_blks);
>   		map.m_len = sec_blks;
>   next_alloc:
>   		f2fs_down_write(&sbi->pin_sem);