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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-51c109d374fsm20272631cf.21.2026.06.30.08.29.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Jun 2026 08:29:40 -0700 (PDT) Date: Tue, 30 Jun 2026 11:29:36 -0400 From: Gregory Price To: "Huang, Ying" Cc: Johannes Weiner , Andrew Morton , David Hildenbrand , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Alistair Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Neha Gholkar Subject: Re: [PATCH] mm: mempolicy: fix automatic numa balancing for shmem Message-ID: References: <20260629163337.1264881-1-hannes@cmpxchg.org> <87h5mkz33h.fsf@DESKTOP-5N7EMDA> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87h5mkz33h.fsf@DESKTOP-5N7EMDA> X-Stat-Signature: 98zdj5o9ziyyjzobepn6365txp3znfab X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: BE66CC0005 X-HE-Tag: 1782833381-721926 X-HE-Meta: U2FsdGVkX192NGgHnUn0qn8k75S2LHGhps13i1Dqs+A42pG30qTYG4Lstev1LAvlSlbrgKWnwO7VkjvY5UyDsAXSvAkRsfyKnNmqzb7P2tX5WOEMFQOcIJcVGFjJYLE0+HJv/iWQ+2UzpFIhq0WI6Ydt64qS/3PTgrd3O+HsBAx7S24/0DGlPOkvSiLEqUrn2bs0e2FGDWbs+0+XoMfwLh8l8/T3msP908dKzZ1+dvxn5XwMAZFGOC65a2EcWQcvbDg6gZi/VBra92WDcYynfuSw/j9373RPbwpIuzS623oTRLOIUt4FNVKn6BN07g6NcTZRflZHJ5i55NbpQsT7vGGWPNzyH4ql9dLEcXl3PqkGFjypMl9ZxPsNGD4+1lbSZdOAaWljFCuriScu9TszwOvdBQiHTI1GACa5OwPMhg39hbRDJgBw6wAyL0wX4UhTRUgw4+0jQzgNt3ob6JpLmE4hb8wJvJoWmKtQGOS9cAQVd+SAb4CxOLY+uza/iwsB4V0HKVTW4BOc1t37DcK6LYe/vI5DZ8pmJ8DJ4/aXjwpfDgQQNV1Z/eJqGnDj44NXGImEWTZVwPOEHhJqsCVcs48Rz4cdrvyOc0MYI3S6f47imcBXphroMAtpCYHWWgJR9mVWyW/+KwcIbhW9bpQ+tVHycgmsuc2YWw7xUB9i6OKELJ2xYBoGJcsYNKdKDyGxANUED4j0PEDQCJbmb6MQwNmO/1rdMcZG/ZB6Ynu/oczPM+M9rZGVZJVh0Uym6jXoMGTr+lJ/u69mtLWrzTSsYtWAx2EP4eCVxnnT5+iSjdGrFGKBI9+es819ZI24E30sIJcung00S+UXWqhAiHB0GBCccrPY1IwPuTbsb8xK+tQD+/kkHKDRHUCHroP/jTz2gVitQXVcl01bh1KS17kQwSiNO2l/1ZNqB6lJIAbDW5zmQQmZRRUHAhOnO2XvXhgx1Cgi9WbZMPLE8z0NUzW J5tYnzGt NETcB3SBqlHTGMxgDdu0bOBKwVr5/S8RVj1bh4PLT2Im/zvSkUGICjiRlIa/30vvhWgmGQqRWWXbCXDeq2V6eKDUD8FTC3aW8t4/I0VaIX2+kJVhv5lvn2J5Vljw3bqcC3cph7jgaLTagrcWGKW0j++RT+idboc6A5wVLfij0QfXbfNV+jF1oYFnu4/l49L7IA7YtT4+FPFSezasx/QWBbt81j+2IpL7u+waHv3AkE3keIx5mU8UCIuPBUPNZ+Oe0W58/xqN3APMsGc8BeYMgd3lf98X8Z9WtsuJqMT8YJaGdVyGKMIbDSI5REEqTWepY+eDy9R4AsyzsLUPrNaiQi2oINuhQMuea8t0WJYN/WsolJpBlykt8qOXw35XmXinJwmrKg/AvrsYETbrZ5Rcoc/igmlvCfAOSHR9kRbfs+8ph++MF7SSjxNQd8f2rKEZDxx2U+7h5c5C9dNGQZ3OFsw6UQw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jun 30, 2026 at 07:20:50PM +0800, Huang, Ying wrote: > Gregory Price writes: > > [snip] > > > Demotions don't care about mempolicy, so opting shmem out of NUMA > > balancing and mbind'ing on a tiered system is just full sadness. > > > > This is all just more evidence that demotion needs to be completely > > redone, it's creating a mess of undefined behavior for memory placement. > > It's hard to respect mempolicy during demotion in the current > implementation. Do you have any ideas on how to improve this? > I think it's feasible we could respect per-vma mempolicies, but not per-task. That would at least make this particular interaction less painful and mbind() would do what you'd expect. It is a bit racy, but with MPOL_MF_MOVE_ALL the user can get what they actually want. I think task-wide mempolicy is problematic and generally a bad idea on tiered systems, maybe it's ok if we simply document task policies are not respected on tiered systems? ~Gregory