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[80.187.83.110]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e7236267bsm153801895e9.16.2025.10.05.23.43.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 05 Oct 2025 23:43:21 -0700 (PDT) Message-ID: <872c98fa-56d8-45cc-a7d2-1b8d44614640@redhat.com> Date: Mon, 6 Oct 2025 08:43:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: always call rmap_walk() on locked folios To: Peter Xu 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 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> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 1C08E180004 X-Stat-Signature: kadkzb9yhjqg9fu1czr5isuqrw6bfmpa X-HE-Tag: 1759733005-250066 X-HE-Meta: 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 vzLmzud4 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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 04.10.25 01:02, Peter Xu wrote: > 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.. I would not trust the docs that much ;) We establish device-private folios when a driver requests to migrate an ordinary (non-zone-device) anonymous folio to device-private memory (e.g., due to a device page fault). When the CPU re-accesses that memory, we spot a device-private entry and trigger migration back from device-private memory to ordinary (CPU-accessible) RAM. The latter is triggered in do_swap_page() where we handle is_device_private_entry() to call pgmap->ops->migrate_to_ram(vmf); For migration and everything around that to work, obviously the device-private page also must be anonymous. It'a s bit more obvious in copy_nonpresent_pte() where we call folio_try_dup_anon_rmap_pte() for is_device_private_entry(), because these are just anonymous folios. -- Cheers David / dhildenb