linux-kernel - Re: [GIT PULL] VFIO updates for v6.17-rc1

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Message-ID: <CAHk-=wg75QKYCCCAtbro5F7rnrwq4xYuKmKeg4hUwuedcPXuGw@mail.gmail.com>
Date: Tue, 5 Aug 2025 16:36:20 +0300
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: David Hildenbrand <david@...hat.com>, Alex Williamson <alex.williamson@...hat.com>, 
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"lizhe.67@...edance.com" <lizhe.67@...edance.com>
Subject: Re: [GIT PULL] VFIO updates for v6.17-rc1

On Tue, 5 Aug 2025 at 16:26, Jason Gunthorpe <jgg@...dia.com> wrote:
>
> David, there is another alternative to prevent this, simple though a
> bit wasteful, just allocate a bit bigger to ensure the allocation
> doesn't end on an exact PAGE_SIZE boundary?

So I don't mind adding a check for "page_section()", because at least
that makes sense.

But yes, it would also probably be a good idea to try to minimize
SPARSEMEM without VMEMMAP. I'd love to get rid of it entirely, of
course, but even if that isn't possible, I'd *really* just like people
to try to make sure that it's neve ra valid thing to try to combine
memory across different sections.

David mentioned the 1GB hugepage folios, and I really thought that
even *those* were all in one section. They *should* be.

Do we have any relevant architectures that still do SPARSEMEM without
VMEMMAP? Because if it's purely some "legacy architecture" thing (ie
x86-32), how about just saying "no 1GB hugepages for you".

Because that whole SPARSEMEM without VMEMMAP is certainly painful even
outside of nth_page, and minimizing the pain sounds sane.

                Linus