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b=Oc+g5iS08BauBBDTqNA6YL7U+mPwbB6i646TPD0vACL0CvFaPzyPiPQ2Yu44ReKMA rla58KElVtFO61BpBrkBWDmU9wWjZFg+0Dn6weN9uCXC/Toz/c3fpq4KUqspweianL aLY9iSKrhUpq1B0mOXbZQGu+qqyV8RmNedkRs1dBUfI83GDbX+y1iQNjaiJ6H5Iux7 Xkc3qxW7lQP73zsWFi+uEWKD4PzRRl65qabODcowiF9vgDX5PRRLuPRbJK7iDrt7PD lQrncXDIHTeAZtD2SFgP0k/LpM4SR4I0v5xz41qBozNZ/suoopHJDKhNszzNkXX1rs G/qMQSG2FFx8Q== Message-ID: <70d46998-a6c6-4c18-b8d7-f813582d3143@kernel.org> Date: Fri, 16 Jan 2026 11:58:44 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/mempolicy: fix mpol_rebind_nodemask() for MPOL_F_NUMA_BALANCING To: Jinjiang Tu , Andrew Morton Cc: 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 References: <20251223110523.1161421-1-tujinjiang@huawei.com> <04b92008-f843-4879-b4a3-608cc5e1de4c@kernel.org> <20260115101252.2e0cbe0559e62b988e5f7151@linux-foundation.org> <1ad31dbd-6743-473d-9f66-a603b91d1e54@huawei.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: o5qsdj7gukp9ocn4jqh3uqem9d3zo4iq X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A8C194000C X-HE-Tag: 1768561131-155907 X-HE-Meta: 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 4TLnDr7s FfoK3EEjJTCbhmcDOxT9vxtqsmSKOHWRFnIGrIXjnTtXCZOLYRfv0SfESM+qOMoBgyt0z7jLZpd+3U0GOMt/Pdjyn59AOP155N13Cj7IfFnrR4S4NHdQLMpkww8Ez2xbWloxAoV54mW2h+vAy4EfyvYDSuIqzzsZCUWe9zl10DrHdhCqM8TUx+ClGxmCLcjSwfzinfMLVkAb4EChSU766ZCiGsXV7SX/Tvo7ZiBsxyIcFxNCIHHPOCmenaC5pG4AyaPYkCKhpIynDxo3x/ivW9zFSuMxN8SlY69EunSt6j5qlXFNRjgIk0q1W62UjnX+QKsEAPM0V2z4S1wdOj1skM1NSdVi9WeiqUy1bmGaT2n75eowiOoL3Quua6STkeISoGI2Heh2Hia4tdxZIb3h5IFnon1KAWJ1DI0ZB0XQ3gY9UeZo= 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 1/16/26 07:43, Jinjiang Tu wrote: > > 在 2026/1/16 2:12, Andrew Morton 写道: >> 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? > > I agree don't backport this patch. Users can only see tasks binding to > wrong NUMA after it's cpuset changes. > > Assuming there are 4 NUMA. task is binding to NUMA1 and it is in root cpuset. > Move the task to a cpuset whose cpuset.mems.effective is 0-1. The task should > still be binded to NUMA1, but is binded to NUMA0 wrongly. Do you think it's easy to write a reproducer to be run in a simple QEMU VM with 4 nodes? -- Cheers David