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Fri, 03 Oct 2025 16:02:49 -0700 (PDT) Received: from x1.local ([142.188.210.50]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-878bdf533b8sm53043906d6.50.2025.10.03.16.02.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Oct 2025 16:02:48 -0700 (PDT) Date: Fri, 3 Oct 2025 19:02:47 -0400 From: Peter Xu To: David Hildenbrand Cc: Lokesh Gidra , Dan Williams , Alistair Popple , akpm@linux-foundation.org, linux-mm@kvack.org, kaleshsingh@google.com, ngeoffray@google.com, jannh@google.com, Lorenzo Stoakes , Harry Yoo , Suren Baghdasaryan , Barry Song , SeongJae Park Subject: Re: [PATCH 1/2] mm: always call rmap_walk() on locked folios Message-ID: References: <20250918055135.2881413-1-lokeshgidra@google.com> <20250918055135.2881413-2-lokeshgidra@google.com> <2c9df5ee-6109-4fa5-b895-ad8e47d34bee@redhat.com> <5549ac3a-20cf-4959-ac53-0a89ed0eadd2@redhat.com> <7305f905-0f81-4268-a3b3-933ac00cdb6a@redhat.com> <4909d194-58b7-4e94-b730-f916100238d3@redhat.com> MIME-Version: 1.0 In-Reply-To: <4909d194-58b7-4e94-b730-f916100238d3@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: jc4RaErfu3QdExScDVT1mtUnIxL3_qyiEpfrjzxn5fM_1759532570 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 6B0F2C0010 X-Stat-Signature: b3j3uuwj4kdga6n7b7epjoqy1g6e8sw9 X-Rspam-User: X-HE-Tag: 1759532572-633384 X-HE-Meta: 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 XLIFqoyj /iC84rTIv6m+aEJ7QDzBFNUJSqxcAS1MBgqDABbReZC//xxlRyUqjT1Xy7JEuAOSvQkNOAPmBsXXYVgr6lVMEP5Vj4kfNUqJ7w0P9U9XS+ibQb5veapaB/67COI82nu5Ugpd2sYcDDk9XZhXCxYBsZ0pCsbo5Z8xYTBlRVu4qHkx2OZ67dFkYoMsM5yg5rDIg8Anh38a5h5NH2SFHXOrsOQm39nQPBZBx9UMhiaamsz+AYlqYvBB3nJUiPP9uta/sKEEkaKhtErjZ7pDW5oE+dfKYcWEELbk6bBYhTLZVDEogKyB5vdPcpTI8VZ5L9PZ3CSCHHmA9fWdUzL+CXULHKECH1yhLPsWO4Jsjba05h77Mp0DgkWid/MUNI65Y8YObSninAzV8ECHOTD11HxQWQhGSCkvZo2paVDUUxkCkk5LGjBXnPS7nmfHJb9OErmkgA3sTurEbtkGNivlbcp7N8YNQTLB8iJxoV6Ii 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 Thu, Oct 02, 2025 at 09:22:45AM +0200, David Hildenbrand wrote: > Staring at mf_generic_kill_procs() once again, we have this > > switch (pgmap->type) { > case MEMORY_DEVICE_PRIVATE: > case MEMORY_DEVICE_COHERENT: > rc = -ENXIO; > goto unlock; > ... > } > > IIRC, all anon device folios are MEMORY_DEVICE_PRIVATE, so we should > actually not succeed in this function and just abort. The doc says: * MEMORY_DEVICE_PRIVATE: * Device memory that is not directly addressable by the CPU: CPU can neither * read nor write private memory. In this case, we do still have struct pages * backing the device memory. Doing so simplifies the implementation, but it is * important to remember that there are certain points at which the struct page * must be treated as an opaque object, rather than a "normal" struct page. It does not intepret to anon private memories, but something that the cpu cannot access.. The only way to inteprete this from reading dax_lock_folio() is folio->mapping should normally points to a real address_space of dax but never an anon_vma, otherwise dax_mapping() looks inproper indeed. So I also agree with the conclusion so far, looks like it should be good to ignore the dax path for this problem. Thanks, -- Peter Xu