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Received: from DESKTOP-5N7EMDA(mailfrom:ying.huang@linux.alibaba.com fp:SMTPD_---0X67dyRL_1782903814 cluster:ay36) by smtp.aliyun-inc.com; Wed, 01 Jul 2026 19:03:35 +0800 From: "Huang, Ying" To: Gregory Price 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 In-Reply-To: (Gregory Price's message of "Tue, 30 Jun 2026 11:29:36 -0400") References: <20260629163337.1264881-1-hannes@cmpxchg.org> <87h5mkz33h.fsf@DESKTOP-5N7EMDA> Date: Wed, 01 Jul 2026 19:03:32 +0800 Message-ID: <877bnfynsr.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Stat-Signature: 9annur6k6hsn9wdo814jezqb7aajee8d X-Rspamd-Queue-Id: 77B92A0012 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1782903820-816204 X-HE-Meta: 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 XVnVqnQ7 cuEwPyPkRdpv9ZU1ZKxVilsZoB2rKWUMOIKr+cd3tVKUX90LUKqnNG7+vSWaIY2IF+VtRqvocR+LW733elO4wXrHRVFmsoKdIEBUJT8Bx7vGgr6zTm9OrBFbcPfFRwo4R/iJsdtMBZuSeO5h2g7G9yBI3pZXXQGtJMDKjJfl0NVeNof3vTsh6G8UkKVYL0V/ZtKmUHIR+ZK063eFpLCy82cO+hUfoYPWKq7F+8GRdx3Htw8yvTXfcmXJPVJ7+krwst2iN22iMgr5myveQph0+DiOB8UZBoMhsTjQLExAkiV4r1i7T9YhpDDe+fVoTO3Z2rmN0ZHf3CUhiMEQo/shkFO/YirtEzXDTQkZXxMfkc+Va9gwkUo40YMwCywMsqoe0PcvzHnTYkvBBpWo9u7JF9HastA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Gregory Price writes: > 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. Yes. Per-vma mempolicy support is possible. > 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? Anyway, it's convenient to use numactl to manage mempolicy. Is it possible to enable NUMA_BALANCING_MEMORY_TIERING for non-default VMAs? If we don't enable NUMA_BALANCING_NORMAL, the overhead should be OK because the page table entries are changed to PROTN_ONE only for pages on the slow tier. Additionally, we may need to consider cpusets. --- Best Regards, Huang, Ying