Размер блока ext4

       -b block-size
              Specify the size of blocks in bytes.  Valid block-size values are 1024, 2048 and 4096 bytes per  block.   If  omitted,
              block-size  is  heuristically  determined  by the filesystem size and the expected usage of the filesystem (see the -T
              option).  If block-size is preceded by a negative sign ('-'), then mke2fs will use heuristics to determine the  appro‐
              priate block size, with the constraint that the block size will be at least block-size bytes.  This is useful for cer‐
              tain hardware devices which require that the blocksize be a multiple of 2k.

$ grep MAX_BLOCK_SIZE /usr/src/linux/fs/ext4/ext4.h
#define EXT4_MAX_BLOCK_SIZE             65536
$ _

# mkfs.ext4 -b 65536 /dev/vg/test 
Warning: blocksize 65536 not usable on most systems.
mke2fs 1.42.1 (17-Feb-2012)
mkfs.ext4: 65536-byte blocks too big for system (max 4096)
Proceed anyway? (y,n) y
Warning: 65536-byte blocks too big for system (max 4096), forced to continue
...

# mount /dev/vg/test /tmp
mount: wrong fs type, bad option, bad superblock on /dev/mapper/vg-test,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

gmesg:
[175015.496515] EXT4-fs (dm-4): bad block size 65536

$ grep -rP '#define\s+PAGE_SHIFT\s+\(?16' /usr/src/linux/arch
/usr/src/linux/arch/powerpc/include/asm/page.h:#define PAGE_SHIFT               16
/usr/src/linux/arch/hexagon/include/asm/page.h:#define PAGE_SHIFT 16
/usr/src/linux/arch/sparc/include/asm/page_64.h:#define PAGE_SHIFT   16
/usr/src/linux/arch/mips/include/asm/page.h:#define PAGE_SHIFT  16
$ _