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

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Message-ID: <CAHk-=whUBuZmRNGCxjnAkFQLO_HVV8SgWEAUg+3z4EARD9MM3Q@mail.gmail.com>
Date: Thu, 20 Nov 2025 10:58:13 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Harry Yoo <harry.yoo@...cle.com>, 
	David Rientjes <rientjes@...gle.com>, Christoph Lameter <cl@...two.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, "linux-mm@...ck.org" <linux-mm@...ck.org>, 
	LKML <linux-kernel@...r.kernel.org>, Christoph Hellwig <hch@...radead.org>
Subject: Re: [GIT PULL] slab fix for 6.18-rc7

On Thu, 20 Nov 2025 at 10:45, Vlastimil Babka <vbabka@...e.cz> 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