"data=writeback" and TRIM don't get along

[Nebojsa Trpkovic <trx.lists@gmail.com>]

Hello.

TRIM command issued to SSD doesn't work with this mount options:

============================
rootfs / rootfs rw 0 0
/dev/root / ext4
rw,noatime,commit=100,barrier=0,nobh,stripe=128,data=writeback,discard 0 0
proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0
rc-svcdir /lib64/rc/init.d tmpfs
rw,nosuid,nodev,noexec,relatime,size=1024k,mode=755 0 0
sysfs /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0
udev /dev tmpfs rw,nosuid,relatime,size=10240k,mode=755 0 0
devpts /dev/pts devpts rw,nosuid,noexec,relatime,gid=5,mode=620 0 0
shm /dev/shm tmpfs rw,nosuid,nodev,noexec,relatime 0 0
============================

Removing "data=writeback" option from /etc/fstab and from rootflags in
kernel boot options results in TRIM working just like it should.

So, the question is:

Is this "data=writeback" and TRIM incompatibility a bug or a feature? :)

Thank you.
Nebojsa Trpkovic