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b=CNXCRKekzJbfxi8M92VZTtFEap1OcAI/bqM5TMhY7xYNtCaBm8CxvdChBwUOFNBK7 vdSglnAbSNG+WBQc4ZDUwet0FFYEyaMXKGcqLnDhdeGbJ606sCaUe2jaFDq0wCoAaW m3DX382m4GpI5aM7uhjcLtO0BcXTGYrxRbkg9Dj2ZLsfr7r9XalJzy+s/yireNBQwy SDW+3qYp2qGI9uW2yzs8rTE/PaUNLTq4bwnIEv3wY+Y7I/bfCpQhthw4bht2SNWlVH oDk1Jw1/PdGCxNzgQALD3a8MputnAe8s+PM2UoBn5jEIoqdsP0VZ5OH8AFIMF0r1Bv 8N3DY06jWRKcg== Message-ID: Date: Thu, 1 Oct 2026 12:45:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 5/7] sched/numa: scan PID-inactive VMAs for promotion To: Gregory Price , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, kas@kernel.org, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, matthew.brost@intel.com, byungchul@sk.com, apopple@nvidia.com, jannh@google.com, pfalcato@suse.de, hannes@cmpxchg.org, shy828301@gmail.com, osalvador@suse.de, raghavendra.kt@amd.com, stable@vger.kernel.org References: <20260930112206.205083-1-gourry@gourry.net> <20260930112206.205083-6-gourry@gourry.net> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: tegj18r41er66ti958yb9fi6u45syffy X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: AEA51140002 X-HE-Tag: 1790851552-905441 X-HE-Meta: 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 ybvwe/2U OddS2hBwbVKpuaekJgiu9xK+dKSKgr7/ckf8XXWOEY1elpYV06kNWE1JMBkG40oWS46dl6AMdWfq4RfFaRTDggELAX16YVVfKkuGrWqSG8CdmsycWTO/ttMwIDWmQKrFEyLwKBvRwGQPdDn90kOZjEkjD5B083vz+6Jbh0L4S3Uc+XGa9j/yl3JW9moGS52FInq+g1DKAe5Dk+gFhBwTU2eu7DLtbpsRQlceaeY9F2FF/tEFe+ZJNXdnGkO7wsrEoZiRvqN3gD52CX5p6GRc7AmOqsXY8zeG61/ER+QVf8wLwS4jH0aU7TgT+YdYY5MsN275wC5yCLwXwfA2RX44u+kMFLkrUUrSuFY6bvT82ywS/1ctACC31XZl5DjKn7HG+ze+0UBO0xKby73ZISMSrPUElifhQHO0DTPiF Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/30/26 13:22, Gregory Price wrote: > From: "Gregory Price (Meta)" > > Commit fc137c0ddab2 ("sched/numa: enhance vma scanning logic") skips > VMAs without recent PID activity. Since only NUMA hint faults record > that activity, the filter can suppress the fault needed to promote hot > slow-tier memory. > > Let memory tiering bypass the PID scan filter. In combined mode, use the > placement decision to restrict top-tier sampling to VMAs that need it, > while inactive VMAs still receive promotion-only scans. > > Make this decision only when a VMA scan starts. placement_due is > evaluated for the current task, and a partially scanned VMA is usually > resumed by a different thread, so re-evaluating it for each chunk would > demote in-progress placement scans and starve large VMAs of placement > sampling in multi-threaded processes. > > Track the last completed placement scan separately from scans of any > kind. Promotion-only scans still update prev_scan_seq, but do not > advance the placement-starvation horizon. > > On a host with 768 GB of DRAM and 256 GB of CXL memory, one large shmem > VMA consumed most scanning activity, while 2,537 other VMAs covering > 84 GB were skipped as inactive. One stand-out result: a hot 20 GB hash > table ended up trapped entirely on CXL and drove CXL bandwidth > utilization beyond sustainable levels - resulting in a large regression. > > With this series, the hot hash table ends up split evenly between DRAM > and CXL, tier residency tracks runtime load, and CXL bandwidth > utilization drops from 45GB/s (maxed) to 5-10GB/s, while DRAM bandwidth > utilization increases from ~200GB/s to 250GB/s+, resulting in major > throughput improvements for the database workload. > > Fixes: fc137c0ddab2 ("sched/numa: enhance vma scanning logic") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Gregory Price (Meta) > --- Acked-by: David Hildenbrand (Arm) -- Cheers, David