linux-kernel - Re: [PATCH RFC 01/14] mm/memory: drop highest_memmap_pfn sanity check in vm_normal

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Message-ID: <CABzRoyaea-qmw4JsA85H4QgRAEPPXWKuq2z2Bi41hEXMKifnjg@mail.gmail.com>
Date: Thu, 3 Jul 2025 22:50:09 +0800
From: Lance Yang <ioworker0@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-mm@...ck.org, nvdimm@...ts.linux.dev, 
	Andrew Morton <akpm@...ux-foundation.org>, Juergen Gross <jgross@...e.com>, 
	Stefano Stabellini <sstabellini@...nel.org>, 
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>, Dan Williams <dan.j.williams@...el.com>, 
	Alistair Popple <apopple@...dia.com>, Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Zi Yan <ziy@...dia.com>, 
	Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>, 
	Barry Song <baohua@...nel.org>, Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, 
	Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, Jann Horn <jannh@...gle.com>, 
	Pedro Falcato <pfalcato@...e.de>
Subject: Re: [PATCH RFC 01/14] mm/memory: drop highest_memmap_pfn sanity check
 in vm_normal_page()

On Tue, Jun 17, 2025 at 11:44 PM David Hildenbrand <david@...hat.com> wrote:
>
> In 2009, we converted a VM_BUG_ON(!pfn_valid(pfn)) to the current
> highest_memmap_pfn sanity check in commit 22b31eec63e5 ("badpage:
> vm_normal_page use print_bad_pte"), because highest_memmap_pfn was
> readily available.
>
> Nowadays, this is the last remaining highest_memmap_pfn user, and this
> sanity check is not really triggering ... frequently.
>
> Let's convert it to VM_WARN_ON_ONCE(!pfn_valid(pfn)), so we can
> simplify and get rid of highest_memmap_pfn. Checking for
> pfn_to_online_page() might be even better, but it would not handle
> ZONE_DEVICE properly.
>
> Do the same in vm_normal_page_pmd(), where we don't even report a
> problem at all ...
>
> What might be better in the future is having a runtime option like
> page-table-check to enable such checks dynamically on-demand. Something
> for the future.
>
> Signed-off-by: David Hildenbrand <david@...hat.com>

LGTM. Feel free to add:
Reviewed-by: Lance Yang <lance.yang@...ux.dev>

Thanks,
Lance