From fc137c0ddab29b591db6a091dc6d7ce20ccb73f2 Mon Sep 17 00:00:00 2001 From: Raghavendra K T Date: Wed, 1 Mar 2023 17:49:01 +0530 Subject: [PATCH] sched/numa: enhance vma scanning logic During Numa scanning make sure only relevant vmas of the tasks are scanned. Before: All the tasks of a process participate in scanning the vma even if they do not access vma in it's lifespan. Now: Except cases of first few unconditional scans, if a process do not touch vma (exluding false positive cases of PID collisions) tasks no longer scan all vma Logic used: 1) 6 bits of PID used to mark active bit in vma numab status during fault to remember PIDs accessing vma. (Thanks Mel) 2) Subsequently in scan path, vma scanning is skipped if current PID had not accessed vma. 3) First two times we do allow unconditional scan to preserve earlier behaviour of scanning. Acknowledgement to Bharata B Rao for initial patch to store pid information and Peter Zijlstra (Usage of test and set bit) Link: https://lkml.kernel.org/r/092f03105c7c1d3450f4636b1ea350407f07640e.1677672277.git.raghavendra.kt@amd.com Signed-off-by: Raghavendra K T Suggested-by: Mel Gorman Cc: David Hildenbrand Cc: Disha Talreja Cc: Ingo Molnar Cc: Mike Rapoport Signed-off-by: Andrew Morton --- include/linux/mm.h | 14 ++++++++++++++ include/linux/mm_types.h | 1 + kernel/sched/fair.c | 19 +++++++++++++++++++ mm/memory.c | 3 +++ 4 files changed, 37 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index 9f08a11b355c..215327daffae 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1686,6 +1686,16 @@ static inline int xchg_page_access_time(struct page *page, int time) last_time = page_cpupid_xchg_last(page, time >> PAGE_ACCESS_TIME_BUCKETS); return last_time << PAGE_ACCESS_TIME_BUCKETS; } + +static inline void vma_set_access_pid_bit(struct vm_area_struct *vma) +{ + unsigned int pid_bit; + + pid_bit = current->pid % BITS_PER_LONG; + if (vma->numab_state && !test_bit(pid_bit, &vma->numab_state->access_pids)) { + __set_bit(pid_bit, &vma->numab_state->access_pids); + } +} #else /* !CONFIG_NUMA_BALANCING */ static inline int page_cpupid_xchg_last(struct page *page, int cpupid) { @@ -1735,6 +1745,10 @@ static inline bool cpupid_match_pid(struct task_struct *task, int cpupid) { return false; } + +static inline void vma_set_access_pid_bit(struct vm_area_struct *vma) +{ +} #endif /* CONFIG_NUMA_BALANCING */ #if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 3e1a42673769..f8cbd8efc7cb 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -477,6 +477,7 @@ struct vma_lock { struct vma_numab_state { unsigned long next_scan; + unsigned long access_pids; }; /* diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7072de1686d5..ef27b5931480 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2928,6 +2928,21 @@ static void reset_ptenuma_scan(struct task_struct *p) p->mm->numa_scan_offset = 0; } +static bool vma_is_accessed(struct vm_area_struct *vma) +{ + /* + * Allow unconditional access first two times, so that all the (pages) + * of VMAs get prot_none fault introduced irrespective of accesses. + * This is also done to avoid any side effect of task scanning + * amplifying the unfairness of disjoint set of VMAs' access. + */ + if (READ_ONCE(current->mm->numa_scan_seq) < 2) + return true; + + return test_bit(current->pid % BITS_PER_LONG, + &vma->numab_state->access_pids); +} + /* * The expensive part of numa migration is done from task_work context. * Triggered from task_tick_numa(). @@ -3046,6 +3061,10 @@ static void task_numa_work(struct callback_head *work) vma->numab_state->next_scan)) continue; + /* Do not scan the VMA if task has not accessed */ + if (!vma_is_accessed(vma)) + continue; + do { start = max(start, vma->vm_start); end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE); diff --git a/mm/memory.c b/mm/memory.c index 9999574a9636..f77fccb5310c 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4661,6 +4661,9 @@ int numa_migrate_prep(struct page *page, struct vm_area_struct *vma, { get_page(page); + /* Record the current PID acceesing VMA */ + vma_set_access_pid_bit(vma); + count_vm_numa_event(NUMA_HINT_FAULTS); if (page_nid == numa_node_id()) { count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);