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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93982db6a95sm207374585a.9.2026.09.04.11.20.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Sep 2026 11:20:15 -0700 (PDT) From: Gregory Price To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, david@kernel.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, 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, raghavendra.kt@amd.com, shy828301@gmail.com, baolin.wang@linux.alibaba.com, osalvador@suse.de Subject: [PATCH 0/2] sched/numa: stop VMA scan filters from gating promotion Date: Fri, 4 Sep 2026 14:20:04 -0400 Message-ID: <20260904182006.1562449-1-gourry@gourry.net> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit task_numa_work() applies a series of VMA-level filters before it will mark a VMA for hint faults. Those filters were written when the hint fault was a socket-residency signal. Skipping a VMA only cost some resolution. Under memory tiering the hint fault is not a signal, it is the mechanism. A folio on the slow tier is considered for promotion only because the scan marked it and something then touched it. A VMA excluded from the scan is excluded from promotion, and stays excluded, because the filters take their input from faults the scan itself produces. Patch 1 covers the per-VMA PID filter, which is self-referential: a VMA needs a hint fault to earn a scan, and a scan to produce a hint fault. Patch 2 covers the read-only file mapping exclusion, whose premise: "if we are never going to migrate the page, it is overhead for no gain" only applies to socket-residency, not tier-residency. Neither patch removes a filter. Patch 1 adds vma->numab_state->slow_only, which restricts one scan of one VMA to folios on non-toptier nodes, and scans the rejected VMAs under it. Patch 2 reuses it. A toptier folio is never marked anywhere the filters would not already have marked it, in any mode, so placement behaviour is unchanged and only promotion candidates are added. On a 768G DRAM + 256G CXL host running two ~430G database services: before - DRAM bandwidth decayed from 200GB/s to 150GB/s, CXL climbed from 5GB/s to 45GB/s and capped, request latency went from 800us to 5ms and tracked CXL bandwidth after - DRAM holds 200-250GB/s, CXL holds 7-10GB/s, request latency sits at 800us-2ms and tracks request load Gregory Price (2): sched/numa: do not let the per-VMA PID filter gate promotion sched/numa: scan read-only file mappings in tiering mode include/linux/mm_types.h | 7 +++++++ kernel/sched/fair.c | 41 ++++++++++++++++++++++++++++++++++------ mm/mempolicy.c | 9 +++++---- 3 files changed, 47 insertions(+), 10 deletions(-) -- 2.55.0