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

["Sunmin Jeong" <s_min.jeong@samsung.com>]

>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@samsung.com>
>> Reviewed-by: Yeongjin Gil <youngjin.gil@samsung.com>
>> Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
>> Signed-off-by: Sunmin Jeong <s_min.jeong@samsung.com>
>> ---
>>   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,

Thanks for your quick reply.
I'll send a v2 patch.

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