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

From: Chao Yu
Date: Tue Jun 25 2024 - 10:13:00 EST


On 2024/6/25 20:15, 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@xxxxxxxx>

Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,