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AJvYcCWJwwxdS9jRF9ImG7fBCcEdQ+KwrObvHUC7qPcI/zMOSoQg9/PsobFGTq0Uf9Kmtnqcbt8uBUdtnA==@kvack.org X-Gm-Message-State: AOJu0YzVqRfyxQCFmIiNKytvQXCdO3Peh6GYe/lVWrlwiGEp7G0J3uVz 7D7jfo6q4tlAdvfo/XBuV8JfFcLYQb4tec4U+w+4C6TT+yPuIAgNp7fI6eEWBzg8gSTtlYhFNV8 qcQDi+ShHELtMjMbib84kokFc19m94U8= X-Gm-Gg: ASbGnct58BdxuqMBkLKTeEsjZ53Za3pWr1h1MHGvlm0r+cX5W2FV521F6ZSJkuD88lC UrRZiR+IFCSN8/+DOy+tGpxFmG8yFkoyd8cgTI66p5srQt1LaBuk2vGo1/6Q62uKOyuTLwWcdJl s11me4EHgfpXRI7ZYl9ymAsnHmSoMvDNZuSW7k5aEmu22HpZteFty9QawkNQ== X-Google-Smtp-Source: AGHT+IGbPYrN54dYrzHXjzvtPMziKIP2dK+ZFdrAB9bFhOzkRz3Vofn+4fvXYD/kf1p6asLy/7oo4AMZVhDjgjTRKGE= X-Received: by 2002:ad4:5cc9:0:b0:700:bc46:5355 with SMTP id 6a1803df08f44-702bcc507bdmr58755466d6.28.1751546065169; Thu, 03 Jul 2025 05:34:25 -0700 (PDT) MIME-Version: 1.0 References: <20250617154345.2494405-1-david@redhat.com> <20250617154345.2494405-2-david@redhat.com> In-Reply-To: From: Lance Yang Date: Thu, 3 Jul 2025 20:34:11 +0800 X-Gm-Features: Ac12FXwlisPZPIPS0YTxEVYIGMNVB3un9rKexLCpMfXXShG5J5pRHWps4sQZYSw Message-ID: Subject: Re: [PATCH RFC 01/14] mm/memory: drop highest_memmap_pfn sanity check in vm_normal_page() To: David Hildenbrand Cc: Oscar Salvador , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, nvdimm@lists.linux.dev, Andrew Morton , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Dan Williams , Alistair Popple , Matthew Wilcox , Jan Kara , Alexander Viro , Christian Brauner , Zi Yan , Baolin Wang , Lorenzo Stoakes , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 344B21C0008 X-Stat-Signature: e1fo5krw7dktybsagktk1o1ms3m5czda X-Rspam-User: X-HE-Tag: 1751546066-118064 X-HE-Meta: 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 WNpms7g1 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 23, 2025 at 10:04=E2=80=AFPM David Hildenbrand wrote: > > On 20.06.25 14:50, Oscar Salvador wrote: > > On Tue, Jun 17, 2025 at 05:43:32PM +0200, David Hildenbrand 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. Somethin= g > >> for the future. > >> > >> Signed-off-by: David Hildenbrand > > > > Hi Oscar, > > > I'm confused, I'm missing something here. > > Before this change we would return NULL if e.g: pfn > highest_memmap_pf= n, but > > now we just print the warning and call pfn_to_page() anyway. > > AFAIK, pfn_to_page() doesn't return NULL? > > You're missing that vm_normal_page_pmd() was created as a copy from > vm_normal_page() [history of the sanity check above], but as we don't > have (and shouldn't have ...) print_bad_pmd(), we made the code look > like this would be something that can just happen. > > " > Do the same in vm_normal_page_pmd(), where we don't even report a > problem at all ... > " > > So we made something that should never happen a runtime sanity check > without ever reporting a problem ... IIUC, the reasoning is that because this case should never happen, we can change the behavior from returning NULL to a "warn and continue" model? Thanks, Lance