Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout

Arnd Bergmann
2025-09-22T21:23:04Z

On Mon, Sep 22, 2025, at 19:05, Nicolas Schichan wrote:
>> On Fri, Sep 19, 2025, at 16:34, Jason Gunthorpe wrote:
>> > On Fri, Sep 19, 2025 at 04:22:20PM +0200, Arnd Bergmann wrote:
>>
>> I did get an email from Nicolas Schichan (added to Cc here),
>> and he is still supporting a widely deployed Kirkwood based
>> platform that uses 1GB RAM configurations. He should get
>> a chance to test that with CONFIG_VMSPLIT_3G_OPT, but I
>> would expect that to continue working, possibly with minor
>> bugfixes.
>
> We don't use HIGMEM on our Kirkwood platform, we are happy using a
> 2G/2G WMSPLIT. We don't need a lot of virtual address space for
> userland, and with the 2G split we don't waste physical memory.

Ok, good.

> I'm happy to test your patch serie with VMSPLIT_3G_OPT and see if it
> still boots with it once you send it.

The patches I did for turning off HIGHMEM on ARMv5 won't have
any effect if you are already running without highmem, so I
don't think we need to wait for your tests specifically.
Any testing would be useful of course just to check that
everything still works.

Jason, I think we can go ahead with your suggestion. I can
post my patches for review once I've done some testing on
them.

Arnd