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Subject[PATCH 18/33] sched, numa, mm: Add the scanning page fault machinery
Date
From: Peter Zijlstra <a.p.zijlstra@chello.nl>

Add the NUMA working set scanning/hinting page fault machinery,
with no policy yet.

The numa_migration_target() function is a derivative of
Andrea Arcangeli's code in the AutoNUMA tree - including the
comment above the function.

An additional enhancement is that instead of node granular faults
we are recording CPU granular faults, which allows us to make
a distinction between:

- 'private' tasks (who access pages that have been accessed
from the same CPU before - i.e. by the same task)

- and 'shared' tasks: who access pages that tend to have been
accessed by another CPU, i.e. another task.

We later on use this fault metric to do enhancement task and
memory placement.

[ The earliest versions had the mpol_misplaced() function from
Lee Schermerhorn - this was heavily modified later on. ]

Many thanks to everyone involved for these great ideas and code.

Written-by: Andrea Arcangeli <aarcange@redhat.com>
Also-written-by: Lee Schermerhorn <lee.schermerhorn@hp.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: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Hugh Dickins <hughd@google.com>
[ split it out of the main policy patch - as suggested by Mel Gorman ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/linux/init_task.h | 8 +++
include/linux/mempolicy.h | 6 +-
include/linux/mm_types.h | 4 ++
include/linux/sched.h | 41 ++++++++++++--
init/Kconfig | 73 +++++++++++++++++++-----
kernel/sched/core.c | 15 +++++
kernel/sysctl.c | 31 ++++++++++-
mm/huge_memory.c | 1 +
mm/mempolicy.c | 137 ++++++++++++++++++++++++++++++++++++++++++++++
9 files changed, 294 insertions(+), 22 deletions(-)

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 6d087c5..ed98982 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -143,6 +143,13 @@ extern struct task_group root_task_group;

#define INIT_TASK_COMM "swapper"

+#ifdef CONFIG_NUMA_BALANCING
+# define INIT_TASK_NUMA(tsk) \
+ .numa_shared = -1,
+#else
+# define INIT_TASK_NUMA(tsk)
+#endif
+
/*
* INIT_TASK is used to set up the first task table, touch at
* your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -210,6 +217,7 @@ extern struct task_group root_task_group;
INIT_TRACE_RECURSION \
INIT_TASK_RCU_PREEMPT(tsk) \
INIT_CPUSET_SEQ \
+ INIT_TASK_NUMA(tsk) \
}


diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index f329306..c511e25 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -198,6 +198,8 @@ static inline int vma_migratable(struct vm_area_struct *vma)
return 1;
}

+extern int mpol_misplaced(struct page *, struct vm_area_struct *, unsigned long);
+
#else

struct mempolicy {};
@@ -323,11 +325,11 @@ static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol,
return 0;
}

-#endif /* CONFIG_NUMA */
-
static inline int mpol_misplaced(struct page *page, struct vm_area_struct *vma,
unsigned long address)
{
return -1; /* no node preference */
}
+
+#endif /* CONFIG_NUMA */
#endif
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 7e9f758..48760e9 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -403,6 +403,10 @@ struct mm_struct {
#ifdef CONFIG_CPUMASK_OFFSTACK
struct cpumask cpumask_allocation;
#endif
+#ifdef CONFIG_NUMA_BALANCING
+ unsigned long numa_next_scan;
+ int numa_scan_seq;
+#endif
struct uprobes_state uprobes_state;
};

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a0a2808..418d405 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1501,6 +1501,18 @@ struct task_struct {
short il_next;
short pref_node_fork;
#endif
+#ifdef CONFIG_NUMA_BALANCING
+ int numa_shared;
+ int numa_max_node;
+ int numa_scan_seq;
+ int numa_migrate_seq;
+ unsigned int numa_scan_period;
+ u64 node_stamp; /* migration stamp */
+ unsigned long numa_weight;
+ unsigned long *numa_faults;
+ struct callback_head numa_work;
+#endif /* CONFIG_NUMA_BALANCING */
+
struct rcu_head rcu;

/*
@@ -1575,7 +1587,25 @@ struct task_struct {
/* Future-safe accessor for struct task_struct's cpus_allowed. */
#define tsk_cpus_allowed(tsk) (&(tsk)->cpus_allowed)

+#ifdef CONFIG_NUMA_BALANCING
+extern void task_numa_fault(int node, int cpu, int pages);
+#else
static inline void task_numa_fault(int node, int cpu, int pages) { }
+#endif /* CONFIG_NUMA_BALANCING */
+
+/*
+ * -1: non-NUMA task
+ * 0: NUMA task with a dominantly 'private' working set
+ * 1: NUMA task with a dominantly 'shared' working set
+ */
+static inline int task_numa_shared(struct task_struct *p)
+{
+#ifdef CONFIG_NUMA_BALANCING
+ return p->numa_shared;
+#else
+ return -1;
+#endif
+}

/*
* Priority of a process goes from 0..MAX_PRIO-1, valid RT
@@ -2014,6 +2044,10 @@ enum sched_tunable_scaling {
};
extern enum sched_tunable_scaling sysctl_sched_tunable_scaling;

+extern unsigned int sysctl_sched_numa_scan_period_min;
+extern unsigned int sysctl_sched_numa_scan_period_max;
+extern unsigned int sysctl_sched_numa_settle_count;
+
#ifdef CONFIG_SCHED_DEBUG
extern unsigned int sysctl_sched_migration_cost;
extern unsigned int sysctl_sched_nr_migrate;
@@ -2024,18 +2058,17 @@ extern unsigned int sysctl_sched_shares_window;
int sched_proc_update_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *length,
loff_t *ppos);
-#endif
-#ifdef CONFIG_SCHED_DEBUG
+
static inline unsigned int get_sysctl_timer_migration(void)
{
return sysctl_timer_migration;
}
-#else
+#else /* CONFIG_SCHED_DEBUG */
static inline unsigned int get_sysctl_timer_migration(void)
{
return 1;
}
-#endif
+#endif /* CONFIG_SCHED_DEBUG */
extern unsigned int sysctl_sched_rt_period;
extern int sysctl_sched_rt_runtime;

diff --git a/init/Kconfig b/init/Kconfig
index cf3e79c..9511f0d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -697,6 +697,65 @@ config HAVE_UNSTABLE_SCHED_CLOCK
bool

#
+# For architectures that (ab)use NUMA to represent different memory regions
+# all cpu-local but of different latencies, such as SuperH.
+#
+config ARCH_WANTS_NUMA_VARIABLE_LOCALITY
+ bool
+
+#
+# For architectures that want to enable NUMA-affine scheduling
+# and memory placement:
+#
+config ARCH_SUPPORTS_NUMA_BALANCING
+ bool
+
+#
+# For architectures that want to reuse the PROT_NONE bits
+# to implement NUMA protection bits:
+#
+config ARCH_WANTS_NUMA_GENERIC_PGPROT
+ bool
+
+config NUMA_BALANCING
+ bool "NUMA-optimizing scheduler"
+ default n
+ depends on ARCH_SUPPORTS_NUMA_BALANCING
+ depends on !ARCH_WANTS_NUMA_VARIABLE_LOCALITY
+ depends on SMP && NUMA && MIGRATION
+ help
+ This option enables NUMA-aware, transparent, automatic
+ placement optimizations of memory, tasks and task groups.
+
+ The optimizations work by (transparently) runtime sampling the
+ workload sharing relationship between threads and processes
+ of long-run workloads, and scheduling them based on these
+ measured inter-task relationships (or the lack thereof).
+
+ ("Long-run" means several seconds of CPU runtime at least.)
+
+ Tasks that predominantly perform their own processing, without
+ interacting with other tasks much will be independently balanced
+ to a CPU and their working set memory will migrate to that CPU/node.
+
+ Tasks that share a lot of data with each other will be attempted to
+ be scheduled on as few nodes as possible, with their memory
+ following them there and being distributed between those nodes.
+
+ This optimization can improve the performance of long-run CPU-bound
+ workloads by 10% or more. The sampling and migration has a small
+ but nonzero cost, so if your NUMA workload is already perfectly
+ placed (for example by use of explicit CPU and memory bindings,
+ or because the stock scheduler does a good job already) then you
+ probably don't need this feature.
+
+ [ On non-NUMA systems this feature will not be active. You can query
+ whether your system is a NUMA system via looking at the output of
+ "numactl --hardware". ]
+
+ Say N if unsure.
+
+#
# Helper Kconfig switches to express compound feature dependencies
# and thus make the .h/.c code more readable:
#
@@ -718,20 +777,6 @@ config ARCH_USES_NUMA_GENERIC_PGPROT_HUGEPAGE
depends on ARCH_USES_NUMA_GENERIC_PGPROT
depends on TRANSPARENT_HUGEPAGE

-#
-# For architectures that (ab)use NUMA to represent different memory regions
-# all cpu-local but of different latencies, such as SuperH.
-#
-config ARCH_WANTS_NUMA_VARIABLE_LOCALITY
- bool
-
-#
-# For architectures that want to enable the PROT_NONE driven,
-# NUMA-affine scheduler balancing logic:
-#
-config ARCH_SUPPORTS_NUMA_BALANCING
- bool
-
menuconfig CGROUPS
boolean "Control Group support"
depends on EVENTFD
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5dae0d2..3611f5f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1544,6 +1544,21 @@ static void __sched_fork(struct task_struct *p)
#ifdef CONFIG_PREEMPT_NOTIFIERS
INIT_HLIST_HEAD(&p->preempt_notifiers);
#endif
+
+#ifdef CONFIG_NUMA_BALANCING
+ if (p->mm && atomic_read(&p->mm->mm_users) == 1) {
+ p->mm->numa_next_scan = jiffies;
+ p->mm->numa_scan_seq = 0;
+ }
+
+ p->numa_shared = -1;
+ p->node_stamp = 0ULL;
+ p->numa_scan_seq = p->mm ? p->mm->numa_scan_seq : 0;
+ p->numa_migrate_seq = 2;
+ p->numa_faults = NULL;
+ p->numa_scan_period = sysctl_sched_numa_scan_period_min;
+ p->numa_work.next = &p->numa_work;
+#endif /* CONFIG_NUMA_BALANCING */
}

/*
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index b0fa5ad..7736b9e 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -256,9 +256,11 @@ static int min_sched_granularity_ns = 100000; /* 100 usecs */
static int max_sched_granularity_ns = NSEC_PER_SEC; /* 1 second */
static int min_wakeup_granularity_ns; /* 0 usecs */
static int max_wakeup_granularity_ns = NSEC_PER_SEC; /* 1 second */
+#ifdef CONFIG_SMP
static int min_sched_tunable_scaling = SCHED_TUNABLESCALING_NONE;
static int max_sched_tunable_scaling = SCHED_TUNABLESCALING_END-1;
-#endif
+#endif /* CONFIG_SMP */
+#endif /* CONFIG_SCHED_DEBUG */

#ifdef CONFIG_COMPACTION
static int min_extfrag_threshold;
@@ -301,6 +303,7 @@ static struct ctl_table kern_table[] = {
.extra1 = &min_wakeup_granularity_ns,
.extra2 = &max_wakeup_granularity_ns,
},
+#ifdef CONFIG_SMP
{
.procname = "sched_tunable_scaling",
.data = &sysctl_sched_tunable_scaling,
@@ -347,7 +350,31 @@ static struct ctl_table kern_table[] = {
.extra1 = &zero,
.extra2 = &one,
},
-#endif
+#endif /* CONFIG_SMP */
+#ifdef CONFIG_NUMA_BALANCING
+ {
+ .procname = "sched_numa_scan_period_min_ms",
+ .data = &sysctl_sched_numa_scan_period_min,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+ {
+ .procname = "sched_numa_scan_period_max_ms",
+ .data = &sysctl_sched_numa_scan_period_max,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+ {
+ .procname = "sched_numa_settle_count",
+ .data = &sysctl_sched_numa_settle_count,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+#endif /* CONFIG_NUMA_BALANCING */
+#endif /* CONFIG_SCHED_DEBUG */
{
.procname = "sched_rt_period_us",
.data = &sysctl_sched_rt_period,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 814e3ea..92e101f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1456,6 +1456,7 @@ static void __split_huge_page_refcount(struct page *page)
page_tail->mapping = page->mapping;

page_tail->index = page->index + i;
+ page_xchg_last_cpu(page, page_last_cpu(page_tail));

BUG_ON(!PageAnon(page_tail));
BUG_ON(!PageUptodate(page_tail));
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index d04a8a5..318043a 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2175,6 +2175,143 @@ static void sp_free(struct sp_node *n)
kmem_cache_free(sn_cache, n);
}

+/*
+ * Multi-stage node selection is used in conjunction with a periodic
+ * migration fault to build a temporal task<->page relation. By
+ * using a two-stage filter we remove short/unlikely relations.
+ *
+ * Using P(p) ~ n_p / n_t as per frequentist probability, we can
+ * equate a task's usage of a particular page (n_p) per total usage
+ * of this page (n_t) (in a given time-span) to a probability.
+ *
+ * Our periodic faults will then sample this probability and getting
+ * the same result twice in a row, given these samples are fully
+ * independent, is then given by P(n)^2, provided our sample period
+ * is sufficiently short compared to the usage pattern.
+ *
+ * This quadric squishes small probabilities, making it less likely
+ * we act on an unlikely task<->page relation.
+ *
+ * Return the best node ID this page should be on, or -1 if it should
+ * stay where it is.
+ */
+static int
+numa_migration_target(struct page *page, int page_nid,
+ struct task_struct *p, int this_cpu,
+ int cpu_last_access)
+{
+ int nid_last_access;
+ int this_nid;
+
+ if (task_numa_shared(p) < 0)
+ return -1;
+
+ /*
+ * Possibly migrate towards the current node, depends on
+ * task_numa_placement() and access details.
+ */
+ nid_last_access = cpu_to_node(cpu_last_access);
+ this_nid = cpu_to_node(this_cpu);
+
+ if (nid_last_access != this_nid) {
+ /*
+ * 'Access miss': the page got last accessed from a remote node.
+ */
+ return -1;
+ }
+ /*
+ * 'Access hit': the page got last accessed from our node.
+ *
+ * Migrate the page if needed.
+ */
+
+ /* The page is already on this node: */
+ if (page_nid == this_nid)
+ return -1;
+
+ return this_nid;
+}
+
+/**
+ * mpol_misplaced - check whether current page node is valid in policy
+ *
+ * @page - page to be checked
+ * @vma - vm area where page mapped
+ * @addr - virtual address where page mapped
+ * @multi - use multi-stage node binding
+ *
+ * Lookup current policy node id for vma,addr and "compare to" page's
+ * node id.
+ *
+ * Returns:
+ * -1 - not misplaced, page is in the right node
+ * node - node id where the page should be
+ *
+ * Policy determination "mimics" alloc_page_vma().
+ * Called from fault path where we know the vma and faulting address.
+ */
+int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long addr)
+{
+ int best_nid = -1, page_nid;
+ int cpu_last_access, this_cpu;
+ struct mempolicy *pol;
+ unsigned long pgoff;
+ struct zone *zone;
+
+ BUG_ON(!vma);
+
+ this_cpu = raw_smp_processor_id();
+ page_nid = page_to_nid(page);
+
+ cpu_last_access = page_xchg_last_cpu(page, this_cpu);
+
+ pol = get_vma_policy(current, vma, addr);
+ if (!(task_numa_shared(current) >= 0))
+ goto out_keep_page;
+
+ switch (pol->mode) {
+ case MPOL_INTERLEAVE:
+ BUG_ON(addr >= vma->vm_end);
+ BUG_ON(addr < vma->vm_start);
+
+ pgoff = vma->vm_pgoff;
+ pgoff += (addr - vma->vm_start) >> PAGE_SHIFT;
+ best_nid = offset_il_node(pol, vma, pgoff);
+ break;
+
+ case MPOL_PREFERRED:
+ if (pol->flags & MPOL_F_LOCAL)
+ best_nid = numa_migration_target(page, page_nid, current, this_cpu, cpu_last_access);
+ else
+ best_nid = pol->v.preferred_node;
+ break;
+
+ case MPOL_BIND:
+ /*
+ * allows binding to multiple nodes.
+ * use current page if in policy nodemask,
+ * else select nearest allowed node, if any.
+ * If no allowed nodes, use current [!misplaced].
+ */
+ if (node_isset(page_nid, pol->v.nodes))
+ goto out_keep_page;
+ (void)first_zones_zonelist(
+ node_zonelist(numa_node_id(), GFP_HIGHUSER),
+ gfp_zone(GFP_HIGHUSER),
+ &pol->v.nodes, &zone);
+ best_nid = zone->node;
+ break;
+
+ default:
+ BUG();
+ }
+
+out_keep_page:
+ mpol_cond_put(pol);
+
+ return best_nid;
+}
+
static void sp_delete(struct shared_policy *sp, struct sp_node *n)
{
pr_debug("deleting %lx-l%lx\n", n->start, n->end);
--
1.7.11.7


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