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

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Message-ID: <c96a97bc-4638-4910-ba27-262fb6cedc96@redhat.com>
Date: Tue, 5 Aug 2025 15:22:04 +0200
From: David Hildenbrand <david@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jason Gunthorpe <jgg@...dia.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 05.08.25 15:15, Linus Torvalds wrote:
> On Tue, 5 Aug 2025 at 16:05, David Hildenbrand <david@...hat.com> wrote:
>>
>> So I don't like the idea of micro-optimizing num_pages_contiguous() by
>> adding weird tweaks to the core for that.
> 
> Seriously - take a look at that suggested sequence I posted, and tell
> me that it isn't *MORE* obvious than the horror that is nth_page().
> 
> Honestly, if anybody thinks nth_page() is obvious and good, I think
> they have some bad case of Stockholm syndrome.
> 
> This isn't about micro-optimizing. This is about not writing complete
> garbage code that makes no sense.
> 
> nth_page() is a disgusting thing that is designed to look up
> known-contiguous pages. That code mis-used it for *testing* for being
> contiguous. It may have _worked_, but it was the wrong thing to do.
> 
> nth_page() in general should just not exist. I don't actually believe
> there is any valid reason for it. I do not believe we should actually
> have valid consecutive allocations of pages across sections.

Oh, just to add to that, 1 GiB folios (hugetlb, dax) are the main reason 
why we use it in things like folio_page(), and also why folio_page_idx() 
is so horrible.

-- 
Cheers,

David / dhildenb