path: root/kernel/sched
diff options
authorPeter Zijlstra <a.p.zijlstra@chello.nl>2012-10-25 14:16:45 +0200
committerMel Gorman <mgorman@suse.de>2012-12-11 14:42:46 +0000
commit6e5fb223e89dbe5cb5c563f8d4a4a0a7d62455a8 (patch)
tree0d5c93240702a51b1d6f22fefd979235a19692fd /kernel/sched
parentcbee9f88ec1b8dd6b58f25f54e4f52c82ed77690 (diff)
mm: sched: numa: Implement constant, per task Working Set Sampling (WSS) rate
Previously, to probe the working set of a task, we'd use a very simple and crude method: mark all of its address space PROT_NONE. That method has various (obvious) disadvantages: - it samples the working set at dissimilar rates, giving some tasks a sampling quality advantage over others. - creates performance problems for tasks with very large working sets - over-samples processes with large address spaces but which only very rarely execute Improve that method by keeping a rotating offset into the address space that marks the current position of the scan, and advance it by a constant rate (in a CPU cycles execution proportional manner). If the offset reaches the last mapped address of the mm then it then it starts over at the first address. The per-task nature of the working set sampling functionality in this tree allows such constant rate, per task, execution-weight proportional sampling of the working set, with an adaptive sampling interval/frequency that goes from once per 100ms up to just once per 8 seconds. The current sampling volume is 256 MB per interval. As tasks mature and converge their working set, so does the sampling rate slow down to just a trickle, 256 MB per 8 seconds of CPU time executed. This, beyond being adaptive, also rate-limits rarely executing systems and does not over-sample on overloaded systems. [ In AutoNUMA speak, this patch deals with the effective sampling rate of the 'hinting page fault'. AutoNUMA's scanning is currently rate-limited, but it is also fundamentally single-threaded, executing in the knuma_scand kernel thread, so the limit in AutoNUMA is global and does not scale up with the number of CPUs, nor does it scan tasks in an execution proportional manner. So the idea of rate-limiting the scanning was first implemented in the AutoNUMA tree via a global rate limit. This patch goes beyond that by implementing an execution rate proportional working set sampling rate that is not implemented via a single global scanning daemon. ] [ Dan Carpenter pointed out a possible NULL pointer dereference in the first version of this patch. ] Based-on-idea-by: Andrea Arcangeli <aarcange@redhat.com> Bug-Found-By: Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Rik van Riel <riel@redhat.com> [ Wrote changelog and fixed bug. ] Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com>
Diffstat (limited to 'kernel/sched')
1 files changed, 52 insertions, 13 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6831abb5dbe..0a349dd1fa6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -780,10 +780,13 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
- * numa task sample period in ms: 5s
+ * numa task sample period in ms
-unsigned int sysctl_numa_balancing_scan_period_min = 5000;
-unsigned int sysctl_numa_balancing_scan_period_max = 5000*16;
+unsigned int sysctl_numa_balancing_scan_period_min = 100;
+unsigned int sysctl_numa_balancing_scan_period_max = 100*16;
+/* Portion of address space to scan in MB */
+unsigned int sysctl_numa_balancing_scan_size = 256;
static void task_numa_placement(struct task_struct *p)
@@ -808,6 +811,12 @@ void task_numa_fault(int node, int pages)
+static void reset_ptenuma_scan(struct task_struct *p)
+ ACCESS_ONCE(p->mm->numa_scan_seq)++;
+ p->mm->numa_scan_offset = 0;
* The expensive part of numa migration is done from task_work context.
* Triggered from task_tick_numa().
@@ -817,6 +826,9 @@ void task_numa_work(struct callback_head *work)
unsigned long migrate, next_scan, now = jiffies;
struct task_struct *p = current;
struct mm_struct *mm = p->mm;
+ struct vm_area_struct *vma;
+ unsigned long offset, end;
+ long length;
WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work));
@@ -846,18 +858,45 @@ void task_numa_work(struct callback_head *work)
if (cmpxchg(&mm->numa_next_scan, migrate, next_scan) != migrate)
- ACCESS_ONCE(mm->numa_scan_seq)++;
- {
- struct vm_area_struct *vma;
+ offset = mm->numa_scan_offset;
+ length = sysctl_numa_balancing_scan_size;
+ length <<= 20;
- down_read(&mm->mmap_sem);
- for (vma = mm->mmap; vma; vma = vma->vm_next) {
- if (!vma_migratable(vma))
- continue;
- change_prot_numa(vma, vma->vm_start, vma->vm_end);
- }
- up_read(&mm->mmap_sem);
+ down_read(&mm->mmap_sem);
+ vma = find_vma(mm, offset);
+ if (!vma) {
+ reset_ptenuma_scan(p);
+ offset = 0;
+ vma = mm->mmap;
+ }
+ for (; vma && length > 0; vma = vma->vm_next) {
+ if (!vma_migratable(vma))
+ continue;
+ /* Skip small VMAs. They are not likely to be of relevance */
+ if (((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) < HPAGE_PMD_NR)
+ continue;
+ offset = max(offset, vma->vm_start);
+ end = min(ALIGN(offset + length, HPAGE_SIZE), vma->vm_end);
+ length -= end - offset;
+ change_prot_numa(vma, offset, end);
+ offset = end;
+ /*
+ * It is possible to reach the end of the VMA list but the last few VMAs are
+ * not guaranteed to the vma_migratable. If they are not, we would find the
+ * !migratable VMA on the next scan but not reset the scanner to the start
+ * so check it now.
+ */
+ if (vma)
+ mm->numa_scan_offset = offset;
+ else
+ reset_ptenuma_scan(p);
+ up_read(&mm->mmap_sem);