Re: [GIT PULL] slab fix for 6.18-rc7

[Linus Torvalds]

On Thu, 20 Nov 2025 at 10:45, Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
> * Fix mempool poisoning order>0 pages with CONFIG_HIGHMEM (Vlastimil Babka)

I've pulled this, but honestly, CONFIG_HIGHMEM should be considered a
dying breed, and I'd have been happier with just not adding extra code
for that thing.

Seriously, CONFIG_HIGHMEM is legacy x86 computers and embedded - old -
arm stuff. Fixing debug code for this is simply not worth it. Nobody
does actual kernel debugging on those platforms.

It already skips poisoning for *much* more important cases, I really
think the whole CONFIG_SLUB_DEBUG_ON could have been conditional on
!CONFIG_HIGHMEM.

In fact, not just SLUB_DEBUG_ON. I suspect *all* of SLUB_DEBUG could
be disabled for non-highmem cases, but I guess that right now it's
only CONFIG_SLUB_DEBUG_ON that triggers this situation anyway.

We will literally get rid of CONFIG_HIGHMEM entirely at some point,
but before we finally get to that point, I think we might as well at
least limit the pain. Because HIGHMEM has always been just that: pain.
Let's not add to it any more.

            Linus