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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-716659a1440sm15515367b3.35.2025.07.06.23.31.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 06 Jul 2025 23:32:02 -0700 (PDT) Date: Sun, 6 Jul 2025 23:31:50 -0700 (PDT) From: Hugh Dickins To: David Hildenbrand cc: Lance Yang , 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 , Lance Yang Subject: Re: [PATCH RFC 01/14] mm/memory: drop highest_memmap_pfn sanity check in vm_normal_page() In-Reply-To: Message-ID: References: <20250617154345.2494405-1-david@redhat.com> <20250617154345.2494405-2-david@redhat.com> <5e5e8d79-61b1-465d-ab5a-4fa82d401215@redhat.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="-1463770367-1279896212-1751869921=:5466" This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. ---1463770367-1279896212-1751869921=:5466 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE On Fri, 4 Jul 2025, David Hildenbrand wrote: > On 03.07.25 16:44, Lance Yang wrote: > > On 2025/7/3 20:39, David Hildenbrand wrote: > >> On 03.07.25 14:34, Lance Yang wrote: > >>> 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. > >>>>>> Something > >>>>>> for the future. > >>>>>> > >>>>>> Signed-off-by: David Hildenbrand The author of 22b31eec63e5 thinks this is not at all an improvement. Of course the condition is not triggering frequently, of course it should not happen: but it does happen, and it still seems worthwhile to catch it in production with a "Bad page map" than to let it run on to whatever kind of crash it hits instead. Hugh ---1463770367-1279896212-1751869921=:5466--