Is your feature request related to a problem? Please describe.
I've been building a multi-tier swap stack on WSL2 (compressed RAM + a userspace block backend for colder pages). On the stock Microsoft kernel both of these show up as off:
# CONFIG_BLK_DEV_UBLK is not set
# CONFIG_ZRAM_WRITEBACK is not set
CONFIG_ZRAM itself is already =m and swap works fine. I/O uring is already on. NBD is there as a module too. So the missing pieces are specifically ublk and zram writeback.
Without them I have to rebuild from https://github.com/microsoft/WSL2-Linux-Kernel every time I want ublk (instead of sitting on NBD only) or attach a writeback device under zram. That works, but it's a lot of friction for something that is already upstream and only needs a config flip.
Describe the solution you'd like
In Microsoft/config-wsl (and arm64 if it applies the same way):
CONFIG_BLK_DEV_UBLK=m
CONFIG_ZRAM_WRITEBACK=y
Module for ublk so it stays out of the way until someone loads it. Writeback only does something if userspace actually sets a backing device.
Describe alternatives you've considered
- Custom kernel from
linux-msft-wsl-6.18.y / 6.6.y with those two options forced on. This works on my machine today.
- Stick to NBD only. Fine for experiments, worse latency/CPU profile than ublk for the same userspace server in my tests.
I'd rather not carry a private kernel long-term if the stock config can ship the modules.
Additional context
Checked against a recent config-wsl from the 6.18.y line. After olddefconfig both options stick cleanly:
CONFIG_BLK_DEV_UBLK=mCONFIG_ZRAM_WRITEBACK=y
No out-of-tree modules involved — just enabling code that is already in the tree you ship.
Happy to retest on a preview kernel if that helps.
Is your feature request related to a problem? Please describe.
I've been building a multi-tier swap stack on WSL2 (compressed RAM + a userspace block backend for colder pages). On the stock Microsoft kernel both of these show up as off:
CONFIG_ZRAMitself is already=mand swap works fine. I/O uring is already on. NBD is there as a module too. So the missing pieces are specifically ublk and zram writeback.Without them I have to rebuild from https://github.com/microsoft/WSL2-Linux-Kernel every time I want ublk (instead of sitting on NBD only) or attach a writeback device under zram. That works, but it's a lot of friction for something that is already upstream and only needs a config flip.
Describe the solution you'd like
In
Microsoft/config-wsl(and arm64 if it applies the same way):Module for ublk so it stays out of the way until someone loads it. Writeback only does something if userspace actually sets a backing device.
Describe alternatives you've considered
linux-msft-wsl-6.18.y/6.6.ywith those two options forced on. This works on my machine today.I'd rather not carry a private kernel long-term if the stock config can ship the modules.
Additional context
Checked against a recent
config-wslfrom the 6.18.y line. Afterolddefconfigboth options stick cleanly:CONFIG_BLK_DEV_UBLK=mCONFIG_ZRAM_WRITEBACK=yNo out-of-tree modules involved — just enabling code that is already in the tree you ship.
Happy to retest on a preview kernel if that helps.