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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 916C1160008 X-Rspamd-Server: rspam09 X-Stat-Signature: 67oeegmsps7pbhncruwphsd683iayh7h X-HE-Tag: 1751632838-424880 X-HE-Meta: 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 xIWOHpc/ 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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 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 PM 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 >>>>> >>>> >>>> Hi Oscar, >>>> >>>>> I'm confused, I'm missing something here. >>>>> Before this change we would return NULL if e.g: pfn > >>>>> highest_memmap_pfn, 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? >> >> Well, yes. Point is, that check should have never been copy-pasted that >> way, while dropping the actual warning :) > > Ah, I see your point now. Thanks for clarifying! I'll add some of that to the patch description. Thanks! -- Cheers, David / dhildenb