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AJvYcCXJeP50DUJFmMYEPaMayOOBPGyXnbGcybTBbS72oSFl5GbdLBMebM/zhT1Ub29sOXWXaKCbIfiACg==@kvack.org X-Gm-Message-State: AOJu0Yz7eZPqdXyr6fkojtgfeUDco4j1liYfFibNlta7R+qpNJ3Jmojn 0Ul/1mzCKPHPFvbYASttVSTJq4zJC89QqdfE6g/JXXEMhG+BLHSL0fSRvQnXvQZSScvkSxSDaLe UE+ZHoLTIg8UQG0pEAs5Ywdbr3cTzbrQwhvumyI2d X-Gm-Gg: ASbGncs9c7jHxT1oKSHWRlrE0TBGFCjxXv1gvF5POTvEbT3m4i88Dwd9UfaS++uCEVl CuaDNVYBclx/DMUBkM0IvXvw7N/tQpnhBJOZ4bGVW9GZuIeLcCC5qf0GLmfI2toPtd8UR607cEX 5igbtTx+bTHvCE9tOAHdz0RpiQWlZkp9SnvchtXAbEev5Glf/scvNTJJHoAokIrRJgqZi8skHLU W+Rx2R1lD/zFfwaYBoVtgEeMTlRhPciUjrmSOdiBTZu X-Google-Smtp-Source: AGHT+IEicMXXtlWGyN6G7V+npJLewUO9XO8YiJmcQ+jrZ8XvJO05E+8ZmlyznHeCsCR1BvtDkyC40A5meCL2FvxyVw8= X-Received: by 2002:aa7:d4ce:0:b0:62f:c78f:d0d4 with SMTP id 4fb4d7f45d1cf-6349bc5d2b5mr36890a12.6.1758741443542; Wed, 24 Sep 2025 12:17:23 -0700 (PDT) MIME-Version: 1.0 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> In-Reply-To: <5549ac3a-20cf-4959-ac53-0a89ed0eadd2@redhat.com> From: Lokesh Gidra Date: Wed, 24 Sep 2025 12:17:11 -0700 X-Gm-Features: AS18NWA_yx_FbzE9Cq77Vt-Azas1zBBSMX6lJsRJSsjkUoBpj9SIA6zlW2o2Yik Message-ID: Subject: Re: [PATCH 1/2] mm: always call rmap_walk() on locked folios To: David Hildenbrand Cc: akpm@linux-foundation.org, linux-mm@kvack.org, kaleshsingh@google.com, ngeoffray@google.com, jannh@google.com, Lorenzo Stoakes , Harry Yoo , Peter Xu , Suren Baghdasaryan , Barry Song , SeongJae Park , Dan Williams , Alistair Popple Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 790051C0009 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: hes1morennszedkwe7qxj8t1835whddy X-HE-Tag: 1758741445-308047 X-HE-Meta: U2FsdGVkX1+HU3bb4HS1GzF39Cvn1CLNyGpj+ABfLG3URBG7C4yP7jreeuQnURQ4LHCSmkINZDmwAA/wEARxmejj+2+bFQQLZbWqYeVAhhtjlZPY6IsKCEemhvmBXyCn+vKqDrAM2OXizGQit02rs7HQSCLiULPg2Thh7/IxRfqOFhIbUhrCg3XfVsvMwVzIve9qlLuO7ab6nwmzXStbvMzNUoB+L+JScSmvJ8wfIyb/6dKCTVVeAsXER5gZdpOJyLfuiUg9KVwU4mTRPZ3eCt0ymWh6iCXXpeJYTXBJqzvnRRjdjV9oW9EvQ6AMSQIGdDZ9QfMC8LlncIxz9g7BZcwwshfVqNPXfQzZ73VVJuFDWqEOBIJ6IqvVFxHMQKwGgxsHtAV6e4YHJsqaxPF0XSvmaKn9M+xi8MEKHkugpiV1sqlxoe/D4vrac+5FfE06Um+qZch8rHkPCgHgiNe0ib0a3xNZtEkxk8iLWA4fc1BvD8N9KQQumcJ9Z8Oa5V8ZF3GMDDUxq+O8hO+/RNO3qRIiuVndpwJMcw9EnKs3ydIlXm4mWJ89oM+i4ebKImfEkpRfPWcmjcnq9jYtDQ7gDTy9nm+6K+CIqbYli0x+WOqndoBT0GW2ZPWY1Mu2kXtzwWwl3ATUGZywyZHqLJpZLuslQ/e3SeVq3hnT6nmHy/BtBFPkQEc5wG139yJlNuk+K9cxiIq1oH/CVCLv24m+Itmjh9Z55t4swtSj+AUGqYhTZxVvtMk4S2lTe22l7/qVSpeTv9WB9uIS97rYyrBc2dV47eXGm5jLW/cR6js5z2oxBQhrvuuSteXuzrqWYrds6mbHwIjdgXGftJJBVMJNRjs0M2zKM+SGmVdSiSxDqIx3/EvImU/hsEBeVPbvNQoBHU7PTfTMzJ3E1Ag9CioJmsqb6n8cKQAs/XiUOckgL88Liebv73on9mNSTWgBarKBjgoXeLJbc0NH1yqlDP+ kP1T9tkZ /7dWRnwbARCCbSB2BclzFnp3IYVO8oNaGdPRYA44KFfFntHvij/OGreg24hJcLuB3V/kbAB5Kjj5qfqb15YTO3tD/MldbIheFn1aIE+rzakegGn1rCQoTlzJ53zEeBZL/Lb68OyFjMtP7V685XC2ZdlM3O4xYKKBxqZ8WSqo/Z7yDuvvQkl3K3L+5JGcf8D5b8AwUNv81D/i0dkexEHeKkboO7OIz5e2GL8WZvT58+nYfQ2FtynB1bawY4QDKrSec8LiQoVvzQ+1B/ZY= 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 Wed, Sep 24, 2025 at 3:00=E2=80=AFAM David Hildenbrand wrote: > > >> > >> Is mf_generic_kill_procs()->collect_procs() problematic? > >> > >> The dax_lock_folio/dax_unlock_folio part confuses me: I think it only > >> locks an entry in the page cache but not the actual folio ("Lock the D= AX > >> entry corresponding to a folio")? > > Yeah. The name dax_lock_folio() gives an impression as if the folio is > > locked but it isn't :) > > Sorry for the late reply, I saw you posted v2 in the meantime. > > > > > IIUC, a dax folio can't have an anon_vma (folio->mapping is actually > > an address_space instead of anon_vma), right? > > We have these weird device-private dax folios that are anonymous and > should have the anon_vma set up. > > > So, I thought it wasn't > > required to actually lock the folio in this case. Please let me know > > if you want me to still lock the folio around collect_procs(), or add > > a comment? > > I think we can end up reaching memory_failure_dev_pagemap() with an > anonymous dax folio. > > Not sure if anything would prevent us into calling > > mf_generic_kill_procs()->collect_procs()->collect_procs_anon()->folio_loc= k_anon_vma_read() > I must be missing something but dax_lock_folio() dereferences folio->mapping (to get to host) without checking for FOLIO_MAPPING_FLAGS presence. If it were an anon folio, wouldn't that be a problem? And then in collect_procs() we obviously check for folio_test_anon() on the same folio before calling collect_procs_anon(). > CCing Dan and AAlistair > > -- > Cheers > > David / dhildenb >