linux启动时提醒unsupported optional features

[SOLVED] couldn't mount because of unsupported optional features (240) 

couldn't mount because of unsupported optional features (240)

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EXT2-fs: sda4 couldn't mount because of unsupported optional features (240)
EXT3-fs: sda4 couldn't mount because of unsupported optional features (240)

When I boot Slackware13.1 it shows this 2 messages but it boots, my fstab says:
/dev/sda3 swap swap defaults 0 0
/dev/sda4 / ext4 defaults 1 1
#/dev/cdrom /mnt/cdrom auto noauto,owner,ro 0 0
#/dev/fd0 /mnt/floppy auto noauto,owner 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
proc /proc proc defaults 0 0
tmpfs /dev/shm tmpfs defaults 0 0

Thats just a warning and can be ingored.
# Append any additional kernel parameters:
append="quiet vt.default_utf8=0 rootfstype=ext4" 

Its happening cause the kernel probes for ext2 and ext3 before ext4.