Re: [PATCH v2] f2fs: only fragment segment in the same section

Jaegeuk Kim
2024-07-09T21:37:53Z

On 06/25, Sheng Yong wrote:
> When new_curseg() is allocating a new segment, if mode=fragment:xxx is
> switched on in large section scenario, __get_next_segno() will select
> the next segno randomly in the range of [0, maxsegno] in order to
> fragment segments.
>
> If the candidate segno is free, get_new_segment() will use it directly
> as the new segment.
>
> However, if the section of the candidate is not empty, and some other
> segments have already been used, and have a different type (e.g NODE)
> with the candidate (e.g DATA), GC will complain inconsistent segment
> type later.
>
> This could be reproduced by the following steps:
>
> dd if=/dev/zero of=test.img bs=1M count=10240
> mkfs.f2fs -s 128 test.img
> mount -t f2fs test.img /mnt -o mode=fragment:block
> echo 1 > /sys/fs/f2fs/loop0/max_fragment_chunk
> echo 512 > /sys/fs/f2fs/loop0/max_fragment_hole
> dd if=/dev/zero of=/mnt/testfile bs=4K count=100
> umount /mnt
>
> F2FS-fs (loop0): Inconsistent segment (4377) type [0, 1] in SSA and SIT
>
> In order to allow simulating segment fragmentation in large section
> scenario, this patch reduces the candidate range:
> * if curseg is the last segment in the section, return curseg->segno
> to make get_new_segment() itself find the next free segment.
> * if curseg is in the middle of the secion, select candicate randomly in
> the range of [curseg + 1, last_seg_in_the_same_section] to keep type
> consistent.
>
> Signed-off-by: Sheng Yong <shengyong@oppo.com>
> ---
> v2: update commit msg
> ---
> fs/f2fs/segment.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index a0ce3d080f80a..55d474f5c2103 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -2782,10 +2782,21 @@ static unsigned int __get_next_segno(struct f2fs_sb_info *sbi, int type)
> {
> struct curseg_info *curseg = CURSEG_I(sbi, type);
> unsigned short seg_type = curseg->seg_type;
> + unsigned int hint;
>
> sanity_check_seg_type(sbi, seg_type);
> - if (f2fs_need_rand_seg(sbi))
> - return get_random_u32_below(MAIN_SECS(sbi) * SEGS_PER_SEC(sbi));
> + if (f2fs_need_rand_seg(sbi)) {
> + if (__is_large_section(sbi)) {
> + hint = GET_SEC_FROM_SEG(sbi, curseg->segno);
> + if (GET_SEC_FROM_SEG(sbi, curseg->segno + 1) != hint)
> + return curseg->segno;
> + return get_random_u32_inclusive(curseg->segno + 1,
> + GET_SEG_FROM_SEC(sbi, hint + 1) - 1);
> + } else {
> + return get_random_u32_below(MAIN_SECS(sbi) *
> + SEGS_PER_SEC(sbi));
> + }
> + }
>
> if (__is_large_section(sbi))
> return curseg->segno;

if (__is_large_section(sbi)) {
if (f2fs_need_rand_seg(sbi)) {
unsigned int hint = GET_SEC_FROM_SEG(sbi, curseg->segno);
if (GET_SEC_FROM_SEG(sbi, curseg->segno + 1) != hint)
return curseg->segno;
return get_random_u32_inclusive(curseg->segno + 1,
GET_SEG_FROM_SEC(sbi, hint + 1) - 1);
}
return curseg->segno;
} else if (f2fs_need_rand_seg(sbi)) {
return get_random_u32_below(MAIN_SECS(sbi) * SEGS_PER_SEC(sbi));
}

> --
> 2.40.1