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b=Lg6cCJZh4pijiIkH59FFPEsm+BnW9TrN4fToQJLndud7ZJ4UuJ6r1gieuWbsHC5qy KmK5Y1mbx52eM1YyF2g545p4WJ8IYwKjTMNYlNPbu508PmAJ0cpaOtMncU3lLn+jqk g/kQieYyNH0gmflJ0FveGmNl1YjMjbmzRTRLW4Yo= Date: Thu, 15 Jan 2026 10:12:52 -0800 From: Andrew Morton To: "David Hildenbrand (Red Hat)" Cc: Jinjiang Tu , akpm@linuxfoundation.org, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, mgorman@suse.de, linux-mm@kvack.org, wangkefeng.wang@huawei.com Subject: Re: [PATCH v3] mm/mempolicy: fix mpol_rebind_nodemask() for MPOL_F_NUMA_BALANCING Message-Id: <20260115101252.2e0cbe0559e62b988e5f7151@linux-foundation.org> In-Reply-To: <04b92008-f843-4879-b4a3-608cc5e1de4c@kernel.org> References: <20251223110523.1161421-1-tujinjiang@huawei.com> <04b92008-f843-4879-b4a3-608cc5e1de4c@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 77B11120004 X-Stat-Signature: g1uc59wh1wgy6aa5rrrkxjs7rc77nigu X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1768500774-195344 X-HE-Meta: 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 MCBBSRXb GWN887OK6+xtkFfxOb7iE6if+ui9IQotbUWV3/23/ogus/ym4GdvZzsxvG381rv4q0X7wOFU0R6Epmy03MCr2yZY/3PN667AqyKSO9qowMaIzOQ2Z+gc65jfNywfksqmAQ1Coe8C+lkFAoNnTYuhsaScyh4FqME04YPGqSjMP5xB+EdXUKyK6TItyxj2XluWn9XEbmGcqgqc0Mf6WQ3yeXyPEMp7EYjyQkmG9QhlQ6U+kHb9ojmE8LrOo51SnwkiYANXsm+rag2jXqeW12my1GCGSZOInm0AM7cp8zngbgxE5nliCll7Al+0aD0Qfiad/F78CUt+cTcvPBq00YalHyCwVwkkp0yWWMd8zl0EFfJpY/YLJsVR+9RBUGve/s/LJPcxz9tR7Xz2koKk= 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, 15 Jan 2026 18:10:51 +0100 "David Hildenbrand (Red Hat)" wrote: > On 12/23/25 12:05, Jinjiang Tu wrote: > > commit bda420b98505 ("numa balancing: migrate on fault among multiple > > bound nodes") adds new flag MPOL_F_NUMA_BALANCING to enable NUMA balancing > > for MPOL_BIND memory policy. > > > > When the cpuset of tasks changes, the mempolicy of the task is rebound by > > mpol_rebind_nodemask(). When MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES > > are both not set, the behaviour of rebinding should be same whenever > > MPOL_F_NUMA_BALANCING is set or not. So, when an application calls > > set_mempolicy() with MPOL_F_NUMA_BALANCING set but both MPOL_F_STATIC_NODES > > and MPOL_F_RELATIVE_NODES cleared, mempolicy.w.cpuset_mems_allowed should > > be set to cpuset_current_mems_allowed nodemask. However, in current > > implementation, mpol_store_user_nodemask() wrongly returns true, causing > > mempolicy->w.user_nodemask to be incorrectly set to the user-specified > > nodemask. Later, when the cpuset of the application changes, > > mpol_rebind_nodemask() ends up rebinding based on the user-specified > > nodemask rather than the cpuset_mems_allowed nodemask as intended. > > > > To fix this, only set mempolicy->w.user_nodemask to the user-specified > > nodemask if MPOL_F_STATIC_NODES or MPOL_F_RELATIVE_NODES is present. > > > > ... > > I glimpsed over it and I think this is the right fix, thanks! > > Acked-by: David Hildenbrand (Red Hat) Cool. I decided this was "not for backporting", but the description of the userspace-visible runtime effects isn't very clear. Jinjiang, can you please advise?