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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93c24889ac9sm37130085a.27.2026.09.22.11.29.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Sep 2026 11:29:38 -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, 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, 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, jannh@google.com, pfalcato@suse.de, hannes@cmpxchg.org, shy828301@gmail.com, raghavendra.kt@amd.com, stable@vger.kernel.org Subject: [PATCH v3 4/7] sched/numa: separate VMA placement from scan continuation Date: Tue, 22 Sep 2026 14:29:25 -0400 Message-ID: <20260922182928.2199090-5-gourry@gourry.net> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260922182928.2199090-1-gourry@gourry.net> References: <20260922182928.2199090-1-gourry@gourry.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Gregory Price (Meta)" vma_is_accessed() returns true both when a VMA needs placement (east-west) sampling and when a VMA is already mid-scan across multiple scan windows. Callers cannot distinguish placement eligibility from scan progress. Rename the helper to vma_needs_placement_scan() and handle continuation state in task_numa_work(). Cache the scan eligibility decision while a VMA is scanned in chunks so a resumed scan retains the existing policy. This separation allows PID-inactive VMAs to be scanned for promotion without treating scan continuation as evidence of placement eligibility. It is a prerequisite for the following fix and must accompany it when backported. Fixes: fc137c0ddab2 ("sched/numa: enhance vma scanning logic") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Gregory Price (Meta) --- include/linux/mm_types.h | 3 +++ kernel/sched/fair.c | 42 ++++++++++++++++++++++++---------------- 2 files changed, 28 insertions(+), 17 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 77c90b1994131..fd35db969bc94 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -803,6 +803,9 @@ struct vma_numab_state { * A VMA is not eligible for scanning if prev_scan_seq == numa_scan_seq */ int prev_scan_seq; + + /* Preserve placement-scan eligibility during an in-progress scan. */ + bool placement_scan; }; #ifdef __HAVE_PFNMAP_TRACKING diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8a4687f67d82f..a2849e72c4e26 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4074,7 +4074,8 @@ static void reset_ptenuma_scan(struct task_struct *p) p->mm->numa_scan_offset = 0; } -static bool vma_is_accessed(struct mm_struct *mm, struct vm_area_struct *vma) +static bool vma_needs_placement_scan(struct mm_struct *mm, + struct vm_area_struct *vma) { unsigned long pids; /* @@ -4090,15 +4091,6 @@ static bool vma_is_accessed(struct mm_struct *mm, struct vm_area_struct *vma) if (test_bit(hash_32(current->pid, ilog2(BITS_PER_LONG)), &pids)) return true; - /* - * Complete a scan that has already started regardless of PID access, or - * some VMAs may never be scanned in multi-threaded applications: - */ - if (mm->numa_scan_offset > vma->vm_start) { - trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_IGNORE_PID); - return true; - } - /* * This vma has not been accessed for a while, and if the number * the threads in the same process is low, which means no other @@ -4133,7 +4125,8 @@ static void task_numa_work(struct callback_head *work) struct vma_iterator vmi; bool vma_pids_skipped; bool vma_pids_forced = false; - bool placement_scan; + bool pid_scan_allowed, placement_due; + bool placement_scan, scan_started; WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work)); @@ -4304,16 +4297,30 @@ static void task_numa_work(struct callback_head *work) } /* - * Do not scan the VMA if task has not accessed it, unless no other - * VMA candidate exists. + * Do not scan the VMA if a task has not accessed it, unless no other + * VMA candidate exists. If a scan is already in-progress, finish it, + * but track continuation separately from starting a new one. */ - if (!vma_pids_forced && !vma_is_accessed(mm, vma)) { - vma_pids_skipped = true; - trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_PID_INACTIVE); - continue; + placement_due = vma_needs_placement_scan(mm, vma); + scan_started = mm->numa_scan_offset > vma->vm_start; + pid_scan_allowed = vma_pids_forced || placement_due; + + if (!pid_scan_allowed) { + if (scan_started) { + trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_IGNORE_PID); + } else { + vma_pids_skipped = true; + trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_PID_INACTIVE); + continue; + } } + /* Keep scan policy stable while processing a VMA in chunks.*/ placement_scan &= numab_mode & NUMA_BALANCING_NORMAL; + if (scan_started) + placement_scan &= vma->numab_state->placement_scan; + + vma->numab_state->placement_scan = placement_scan; cp_flags = MM_CP_PROT_NUMA; if (!placement_scan) cp_flags |= MM_CP_PROT_NUMA_PROMO_ONLY; @@ -4346,6 +4353,7 @@ static void task_numa_work(struct callback_head *work) /* VMA scan is complete, do not scan until next sequence. */ vma->numab_state->prev_scan_seq = mm->numa_scan_seq; + vma->numab_state->placement_scan = false; /* * Only force scan within one VMA at a time, to limit the -- 2.53.0-Meta