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catalin.marinas@arm.com, will@kernel.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, willy@infradead.org, baohua@kernel.org, dev.jain@arm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 4/5] arm64: mm: implement the architecture-specific clear_flush_young_ptes() Message-ID: References: <9d866a2644051e13a41ef4d6ca3909c6e1f9e229.1766631066.git.baolin.wang@linux.alibaba.com> <20260128114936.72280-1-clm@meta.com> <07d55759-a50a-457a-badd-85697174116f@kernel.org> <280ae63e-d66e-438f-8045-6c870420fe76@linux.alibaba.com> <16fb7985-ec0f-4b56-91e7-404c5114f899@kernel.org> <6817c7b9-e67c-46b6-b3b5-1bc3d9eed4a2@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 vfSyhhce 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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 2026-02-09 at 21:13 +1100, Baolin Wang wrote... > > > On 2/9/26 5:55 PM, David Hildenbrand (Arm) wrote: > > On 2/9/26 10:36, Baolin Wang wrote: > > > > > > > > > On 2/9/26 5:09 PM, David Hildenbrand (Arm) wrote: > > > > On 1/29/26 02:42, Baolin Wang wrote: > > > > > > > > > > > > > > > > > > > > Indeed. I previously discussed with Ryan whether using > > > > > pte_cont() was enough, and we believed that invalid PTEs > > > > > wouldn’t have the PTE_CONT bit set. But we clearly missed > > > > > the device-folio cases. Thanks for reporting. > > > > > > > > > > Andrew, could you please squash the following fix into this > > > > > patch? If you prefer a new version, please let me know. > > > > > Thanks. > > > > > > > > Isn't the real problem that we should never ever ever ever, try > > > > clearing the young bit on a non-present pte? > > > > > > > > See damon_ptep_mkold() how that is handled with the flushing/notify. > > > > > > > > There needs to be a pte_present() check in the caller. > > > > > > The handling of ZONE_DEVICE memory in check_pte() makes me me doubt > > > my earlier understanding. And I think you are right. > > > > > >      } else if (pte_present(ptent)) { > > >          pfn = pte_pfn(ptent); > > >      } else { > > >          const softleaf_t entry = softleaf_from_pte(ptent); > > > > > >          /* Handle un-addressable ZONE_DEVICE memory */ > > >          if (!softleaf_is_device_private(entry) && > > >              !softleaf_is_device_exclusive(entry)) > > >              return false; > > > > > >          pfn = softleaf_to_pfn(entry); > > >      } > > > > > > > > > > BUT > > > > > > > > I recall that folio_referenced() should never apply to > > > > ZONE_DEVICE folios. folio_referenced() is only called from > > > > memory reclaim code, and ZONE_DEVICE pages never get reclaimed > > > > through vmscan.c Agree this is true, although I've always found the reason somewhat difficult to see in code because there are no explicit checks for ZONE_DEVICE pages. Instead it relies on the fact ZONE_DEVICE pages can't be put on any LRU in the first place, hence reclaim can't find them. > > > > > > Thanks for clarifying. So I can drop the pte valid check. > > > > We should probably add a safety check in folio_referenced(), warning > > if we would ever get a ZONE_DEVICE folio passed. > > > > Can someone look into that ? :) > > Sure, I can take a close look and address that in my follow-up patchset. >