ZFS 2.0.1 cannot load zzstd.ko kernel module

Hello,
I have been using ZFS on Linux on slackware for a long time. I run Slackware 14.2 with all updates (not -current). 4.4.240 on most machines, 1 machine on 5.4.85
Since ZFS version 2.0 they have integrated all ZFS code for BSD and Illumos with the Linux ZFS code (so they will have to maintain only 1 instead of several).

I always compile using the autogen.sh script, then ./configure then make and make install and this worked fine upto now (ZFS 0.8.6). With zfs 2.0 a new kernel module zzstd.ko is delivered for "standard" compression which is apparently better then the lz4 which I used upto now.
So I do the same as before. Autogen, configure make and make install. No errors.
When I now do modprobe zfs to load the kernel modules it fails and it complains in the dmesg like this :

Code:[1409015.059597] zfs: Unknown symbol zfs_zstd_compress (err 0)
[1409015.060480] zfs: Unknown symbol zfs_zstd_decompress_level (err 0)
[1409015.061436] zfs: Unknown symbol zfs_zstd_cache_reap_now (err 0)
[1409015.061883] zfs: Unknown symbol zfs_zstd_decompress (err 0)So it seems that the zzstd.ko is not loaded.
When I do modprobe zzstd.ko it says
modprobe: FATAL: Module zzstd.ko not found in directory /lib/modules/4.4.240

But it is there under extra :
Code:root@riwixeon:/lib/modules/4.4.240# ls -alR extra
extra:
total 44
drwxr-xr-x 11 root root 4096 Jan 7 21:49 ./
drwxr-xr-x 4 root root 4096 Dec 22 14:39 ../
drwxr-xr-x 2 root root 4096 Dec 22 14:33 avl/
drwxr-xr-x 2 root root 4096 Dec 22 14:33 icp/
drwxr-xr-x 2 root root 4096 Dec 22 14:33 lua/
drwxr-xr-x 2 root root 4096 Dec 22 14:33 nvpair/
drwxr-xr-x 2 root root 4096 Dec 22 14:33 spl/
drwxr-xr-x 2 root root 4096 Dec 22 14:33 unicode/
drwxr-xr-x 2 root root 4096 Dec 22 14:33 zcommon/
drwxr-xr-x 2 root root 4096 Dec 22 14:33 zfs/
drwxr-xr-x 2 root root 4096 Jan 7 21:49 zstd/

extra/avl:
-rw-r--r-- 1 root root 11264 Jan 7 22:35 zavl.ko

extra/icp:
-rw-r--r-- 1 root root 356592 Jan 7 22:35 icp.ko

extra/lua:
-rw-r--r-- 1 root root 225800 Jan 7 22:35 zlua.ko

extra/nvpair:
-rw-r--r-- 1 root root 106288 Jan 7 22:35 znvpair.ko

extra/spl:
-rw-r--r-- 1 root root 152096 Jan 7 22:35 spl.ko

extra/unicode:
-rw-r--r-- 1 root root 328256 Jan 7 22:35 zunicode.ko

extra/zcommon:
-rw-r--r-- 1 root root 110432 Jan 7 22:35 zcommon.ko

extra/zfs:
-rw-r--r-- 1 root root 3663488 Jan 7 22:35 zfs.ko

extra/zstd:
-rw-r--r-- 1 root root 521104 Jan 7 22:24 zzstd.koWhen I look in the modules.symbols I cannot see any reference to zstd. So I added these :
Code:alias symbol:zfs_zstd_compress zzstd
alias symbol:zfs_zstd_decompress_level zzstd
alias symbol:zfs_zstd_cache_reap_now zzstd
alias symbol:zfs_zstd_decompress zzstdI have also tried to add the zzstd to the modules.dep :
Code:grep zstd modules.dep
modules.dep:extra/zfs/zfs.ko: extra/zstd/zzstd.ko extra/unicode/zunicode.ko extra/lua/zlua.ko extra/zcommon/zcommon.ko extra/nvpair/znvpair.ko extra/avl/zavl.ko extra/icp/icp.ko extra/spl/spl.ko
But still zzstd will not load. And as a result zfs will not load.
I have reverted back to 0.8.6 for now (no zzstd and zfs loads fine with all depending modules).

Does anyone have any hints or tips about what is wrong here?
I do not read about any other distribution users having this issue.
Could it be a problem in ZFS? Or something not compatible with the way slackware handles the kernel module loading?