linux-kernel - Re: [PATCH v4 05/13] mm/arch: Provide pud

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Date: Thu, 4 Apr 2024 08:00:47 -0400
From: Peter Xu <peterx@...hat.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Nathan Chancellor <nathan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Yang Shi <shy828301@...il.com>,
	"Kirill A . Shutemov" <kirill@...temov.name>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	John Hubbard <jhubbard@...dia.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Andrew Jones <andrew.jones@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	linux-riscv@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Lorenzo Stoakes <lstoakes@...il.com>,
	Matthew Wilcox <willy@...radead.org>,
	Rik van Riel <riel@...riel.com>,
	linux-arm-kernel@...ts.infradead.org,
	Andrea Arcangeli <aarcange@...hat.com>,
	David Hildenbrand <david@...hat.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	James Houghton <jthoughton@...gle.com>,
	Mike Rapoport <rppt@...nel.org>,
	Axel Rasmussen <axelrasmussen@...gle.com>,
	Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev
Subject: Re: [PATCH v4 05/13] mm/arch: Provide pud_pfn() fallback

On Thu, Apr 04, 2024 at 08:24:04AM -0300, Jason Gunthorpe wrote:
> On Wed, Apr 03, 2024 at 02:25:20PM -0400, Peter Xu wrote:
> 
> > > I'd say the BUILD_BUG has done it's job and found an issue, fix it by
> > > not defining pud_leaf? I don't see any calls to pud_leaf in loongarch
> > > at least
> > 
> > Yes, that sounds better too to me, however it means we may also risk other
> > archs that can fail another defconfig build.. and I worry I bring trouble
> > to multiple such cases.  Fundamentally it's indeed my patch that broke
> > those builds, so I still sent the change and leave that for arch developers
> > to decide the best for the archs.
> 
> But your change causes silent data corruption if the code path is
> run.. I think we are overall better to wade through the compile time
> bugs from linux-next. Honestly if there were alot then I'd think there
> would be more complaints already.
> 
> Maybe it should just be a seperate step from this series.

Right, that'll be imho better to be done separate, as I think we'd better
consolidate the code.

One thing I don't worry is the warning would cause anything real to fail; I
don't yet expect any arch that will not define pud_pfn when it needs
it.. so it can mean all of the build errors may not cause real benefits as
of now.  But I agree with you we'd better have it.  I'll take a todo and
I'll try to add it back after all these fallouts.  With my cross build
chains now it shouldn't be hard, just take some time to revisit each arch.

Thanks,

-- 
Peter Xu