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[2003:cb:c738:3100:8133:26cf:7877:94aa]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a8e320329sm15298458f8f.0.2025.01.14.08.45.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Jan 2025 08:45:48 -0800 (PST) Message-ID: <86efded9-c1d9-4efb-bf41-f67faa49bf69@redhat.com> Date: Tue, 14 Jan 2025 17:45:46 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 19/26] proc/task_mmu: Mark devdax and fsdax pages as always unpinned To: Dan Williams , Alistair Popple , akpm@linux-foundation.org, linux-mm@kvack.org Cc: alison.schofield@intel.com, lina@asahilina.net, zhang.lyra@gmail.com, gerald.schaefer@linux.ibm.com, vishal.l.verma@intel.com, dave.jiang@intel.com, logang@deltatee.com, bhelgaas@google.com, jack@suse.cz, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, mpe@ellerman.id.au, npiggin@gmail.com, dave.hansen@linux.intel.com, ira.weiny@intel.com, willy@infradead.org, djwong@kernel.org, tytso@mit.edu, linmiaohe@huawei.com, peterx@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, david@fromorbit.com, chenhuacai@kernel.org, kernel@xen0n.name, loongarch@lists.linux.dev References: <6785cbb7125bf_20fa29418@dwillia2-xfh.jf.intel.com.notmuch> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250114_084554_579264_9BAA04BA X-CRM114-Status: GOOD ( 15.30 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 14.01.25 03:28, Dan Williams wrote: > Alistair Popple wrote: >> The procfs mmu files such as smaps and pagemap currently ignore devdax and >> fsdax pages because these pages are considered special. A future change >> will start treating these as normal pages, meaning they can be exposed via >> smaps and pagemap. >> >> The only difference is that devdax and fsdax pages can never be pinned for >> DMA via FOLL_LONGTERM, so add an explicit check in pte_is_pinned() to >> reflect that. > > I don't understand this patch. This whole pte_is_pinned() should likely be ripped out (and I have a patch here to do that for a long time). But that's a different discussion. > > pin_user_pages() is also used for Direct-I/O page pinning, so the > comment about FOLL_LONGTERM is wrong, and I otherwise do not understand > what goes wrong if the only pte_is_pinned() user correctly detects the > pin state? Yes, this patch should likely just be dropped. Even if folio_maybe_dma_pinned() == true because of "false positives", it will behave just like other order-0 pages with false positives, and only affect soft-dirty tracking ... which nobody should be caring about here at all. We would always detect the PTE as soft-dirty because we we never pte_wrprotect(old_pte) Yes, nobody should care. -- Cheers, David / dhildenb