Can't find correct configuration

[Leon Pollak]

Hello, all.
I will be very very thankful for the help to find the correct
configuration for my NAND.
I passed through a lot of mails in the lists and google and ChatGPT -
no success.
I have 256MB NAND and 248MB partition for UBIFS. I run:
mkfs.ubifs -v -r rootfs -F -m 2048 -e 126976 -c 1981 -o ./ubifs.img
ubinize -v -o rootfs.img -m 2048 -p 128KiB -s 512 -O 2048 ubinize.cfg
-----
and ubinize.cfg looks like:
[ubifs]
mode=ubi
image=./ubifs.img
vol_id=0
vol_size=240MiB
vol_type=dynamic
vol_name=ubi_rootfs
vol_alignment=1
vol_flags=autoresize
------
Kernel configuration  was with CONFIG_MTD_UBI_BEB_LIMIT=20.
and here is the kernel log:
[    2.695659] ubi0: attaching mtd4
[    3.372343] ubi0: scanning is finished
[    3.383066] ubi0 warning: ubi_eba_init: cannot reserve enough PEBs
for bad PEB handling, reserved 4, need 40
[    3.404320] ubi0: volume 0 ("ubi_rootfs") re-sized from 1982 to 1982 LEBs
[    3.411667] ubi0: attached mtd4 (name "FS", size 248 MiB)
[    3.417095] ubi0: PEB size: 131072 bytes (128 KiB), LEB size: 126976 bytes
[    3.424006] ubi0: min./max. I/O unit sizes: 2048/2048, sub-page size 512
[    3.430740] ubi0: VID header offset: 2048 (aligned 2048), data offset: 4096
[    3.437734] ubi0: good PEBs: 1990, bad PEBs: 0, corrupted PEBs: 0
[    3.443860] ubi0: user volume: 1, internal volumes: 1, max. volumes
count: 128
[    3.451117] ubi0: max/mean erase counter: 1/0, WL threshold: 4096,
image sequence number: 1590570073
[    3.460295] ubi0: available PEBs: 0, total reserved PEBs: 1990,
PEBs reserved for bad PEB handling: 4
[    3.469575] ubi0: background thread "ubi_bgt0d" started, PID 131
[    4.648718] UBIFS (ubi0:0): background thread "ubifs_bgt0_0" started, PID 136
[    4.676640] UBIFS (ubi0:0): start fixing up free space
[   10.250099] UBIFS (ubi0:0): free space fixup complete
[   10.269046] UBIFS (ubi0:0): UBIFS: mounted UBI device 0, volume 0,
name "ubi_rootfs"
[   10.276830] UBIFS (ubi0:0): LEB size: 126976 bytes (124 KiB),
min./max. I/O unit sizes: 2048 bytes/2048 bytes
[   10.286794] UBIFS (ubi0:0): FS size: 250142720 bytes (238 MiB, 1970
LEBs), journal size 9023488 bytes (8 MiB, 72 LEBs)
[   10.297540] UBIFS (ubi0:0): reserved for root: 0 bytes (0 KiB)
[   10.303406] UBIFS (ubi0:0): media format: w4/r0 (latest is w5/r0),
UUID A14D586A-32E2-45D7-A07E-BDC472FDF31D, small LPT model

My question is: why does this warning about reserved 4, needed 40
appear? How can I solve this?

Many thanks for the help!

LP