kernel/sched/fair.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Completely Fair Scheduling (CFS) Class (SCHED_NORMAL/SCHED_BATCH)
 *
 *  Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 *  Interactivity improvements by Mike Galbraith
 *  (C) 2007 Mike Galbraith <efault@gmx.de>
 *
 *  Various enhancements by Dmitry Adamushko.
 *  (C) 2007 Dmitry Adamushko <dmitry.adamushko@gmail.com>
 *
 *  Group scheduling enhancements by Srivatsa Vaddagiri
 *  Copyright IBM Corporation, 2007
 *  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
 *
 *  Scaled math optimizations by Thomas Gleixner
 *  Copyright (C) 2007, Thomas Gleixner <tglx@linutronix.de>
 *
 *  Adaptive scheduling granularity, math enhancements by Peter Zijlstra
 *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
 */
#include <linux/energy_model.h>
#include <linux/mmap_lock.h>
#include <linux/hugetlb_inline.h>
#include <linux/jiffies.h>
#include <linux/mm_api.h>
#include <linux/highmem.h>
#include <linux/spinlock_api.h>
#include <linux/cpumask_api.h>
#include <linux/lockdep_api.h>
#include <linux/softirq.h>
#include <linux/refcount_api.h>
#include <linux/topology.h>
#include <linux/sched/clock.h>
#include <linux/sched/cond_resched.h>
#include <linux/sched/cputime.h>
#include <linux/sched/isolation.h>
#include <linux/sched/nohz.h>

#include <linux/cpuidle.h>
#include <linux/interrupt.h>
#include <linux/memory-tiers.h>
#include <linux/mempolicy.h>
#include <linux/mutex_api.h>
#include <linux/profile.h>
#include <linux/psi.h>
#include <linux/ratelimit.h>
#include <linux/task_work.h>
#include <linux/rbtree_augmented.h>

#include <asm/switch_to.h>

#include "sched.h"
#include "stats.h"
#include "autogroup.h"

/*
 * The initial- and re-scaling of tunables is configurable
 *
 * Options are:
 *
 *   SCHED_TUNABLESCALING_NONE - unscaled, always *1
 *   SCHED_TUNABLESCALING_LOG - scaled logarithmically, *1+ilog(ncpus)
 *   SCHED_TUNABLESCALING_LINEAR - scaled linear, *ncpus
 *
 * (default SCHED_TUNABLESCALING_LOG = *(1+ilog(ncpus))
 */
unsigned int sysctl_sched_tunable_scaling = SCHED_TUNABLESCALING_LOG;

/*
 * Minimal preemption granularity for CPU-bound tasks:
 *
 * (default: 0.75 msec * (1 + ilog(ncpus)), units: nanoseconds)
 */
unsigned int sysctl_sched_base_slice			= 750000ULL;
static unsigned int normalized_sysctl_sched_base_slice	= 750000ULL;

const_debug unsigned int sysctl_sched_migration_cost	= 500000UL;

static int __init setup_sched_thermal_decay_shift(char *str)
{
	pr_warn("Ignoring the deprecated sched_thermal_decay_shift= option\n");
	return 1;
}
__setup("sched_thermal_decay_shift=", setup_sched_thermal_decay_shift);

#ifdef CONFIG_SMP
/*
 * For asym packing, by default the lower numbered CPU has higher priority.
 */
int __weak arch_asym_cpu_priority(int cpu)
{
	return -cpu;
}

/*
 * The margin used when comparing utilization with CPU capacity.
 *
 * (default: ~20%)
 */
#define fits_capacity(cap, max)	((cap) * 1280 < (max) * 1024)

/*
 * The margin used when comparing CPU capacities.
 * is 'cap1' noticeably greater than 'cap2'
 *
 * (default: ~5%)
 */
#define capacity_greater(cap1, cap2) ((cap1) * 1024 > (cap2) * 1078)
#endif

#ifdef CONFIG_CFS_BANDWIDTH
/*
 * Amount of runtime to allocate from global (tg) to local (per-cfs_rq) pool
 * each time a cfs_rq requests quota.
 *
 * Note: in the case that the slice exceeds the runtime remaining (either due
 * to consumption or the quota being specified to be smaller than the slice)
 * we will always only issue the remaining available time.
 *
 * (default: 5 msec, units: microseconds)
 */
static unsigned int sysctl_sched_cfs_bandwidth_slice		= 5000UL;
#endif

#ifdef CONFIG_NUMA_BALANCING
/* Restrict the NUMA promotion throughput (MB/s) for each target node. */
static unsigned int sysctl_numa_balancing_promote_rate_limit = 65536;
#endif

#ifdef CONFIG_SYSCTL
static struct ctl_table sched_fair_sysctls[] = {
#ifdef CONFIG_CFS_BANDWIDTH
	{
		.procname       = "sched_cfs_bandwidth_slice_us",
		.data           = &sysctl_sched_cfs_bandwidth_slice,
		.maxlen         = sizeof(unsigned int),
		.mode           = 0644,
		.proc_handler   = proc_dointvec_minmax,
		.extra1         = SYSCTL_ONE,
	},
#endif
#ifdef CONFIG_NUMA_BALANCING
	{
		.procname	= "numa_balancing_promote_rate_limit_MBps",
		.data		= &sysctl_numa_balancing_promote_rate_limit,
		.maxlen		= sizeof(unsigned int),
		.mode		= 0644,
		.proc_handler	= proc_dointvec_minmax,
		.extra1		= SYSCTL_ZERO,
	},
#endif /* CONFIG_NUMA_BALANCING */
};

static int __init sched_fair_sysctl_init(void)
{
	register_sysctl_init("kernel", sched_fair_sysctls);
	return 0;
}
late_initcall(sched_fair_sysctl_init);
#endif

static inline void update_load_add(struct load_weight *lw, unsigned long inc)
{
	lw->weight += inc;
	lw->inv_weight = 0;
}

static inline void update_load_sub(struct load_weight *lw, unsigned long dec)
{
	lw->weight -= dec;
	lw->inv_weight = 0;
}

static inline void update_load_set(struct load_weight *lw, unsigned long w)
{
	lw->weight = w;
	lw->inv_weight = 0;
}

/*
 * Increase the granularity value when there are more CPUs,
 * because with more CPUs the 'effective latency' as visible
 * to users decreases. But the relationship is not linear,
 * so pick a second-best guess by going with the log2 of the
 * number of CPUs.
 *
 * This idea comes from the SD scheduler of Con Kolivas:
 */
static unsigned int get_update_sysctl_factor(void)
{
	unsigned int cpus = min_t(unsigned int, num_online_cpus(), 8);
	unsigned int factor;

	switch (sysctl_sched_tunable_scaling) {
	case SCHED_TUNABLESCALING_NONE:
		factor = 1;
		break;
	case SCHED_TUNABLESCALING_LINEAR:
		factor = cpus;
		break;
	case SCHED_TUNABLESCALING_LOG:
	default:
		factor = 1 + ilog2(cpus);
		break;
	}

	return factor;
}

static void update_sysctl(void)
{
	unsigned int factor = get_update_sysctl_factor();

#define SET_SYSCTL(name) \
	(sysctl_##name = (factor) * normalized_sysctl_##name)
	SET_SYSCTL(sched_base_slice);
#undef SET_SYSCTL
}

void __init sched_init_granularity(void)
{
	update_sysctl();
}

#define WMULT_CONST	(~0U)
#define WMULT_SHIFT	32

static void __update_inv_weight(struct load_weight *lw)
{
	unsigned long w;

	if (likely(lw->inv_weight))
		return;

	w = scale_load_down(lw->weight);

	if (BITS_PER_LONG > 32 && unlikely(w >= WMULT_CONST))
		lw->inv_weight = 1;
	else if (unlikely(!w))
		lw->inv_weight = WMULT_CONST;
	else
		lw->inv_weight = WMULT_CONST / w;
}

/*
 * delta_exec * weight / lw.weight
 *   OR
 * (delta_exec * (weight * lw->inv_weight)) >> WMULT_SHIFT
 *
 * Either weight := NICE_0_LOAD and lw \e sched_prio_to_wmult[], in which case
 * we're guaranteed shift stays positive because inv_weight is guaranteed to
 * fit 32 bits, and NICE_0_LOAD gives another 10 bits; therefore shift >= 22.
 *
 * Or, weight =< lw.weight (because lw.weight is the runqueue weight), thus
 * weight/lw.weight <= 1, and therefore our shift will also be positive.
 */
static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight *lw)
{
	u64 fact = scale_load_down(weight);
	u32 fact_hi = (u32)(fact >> 32);
	int shift = WMULT_SHIFT;
	int fs;

	__update_inv_weight(lw);

	if (unlikely(fact_hi)) {
		fs = fls(fact_hi);
		shift -= fs;
		fact >>= fs;
	}

	fact = mul_u32_u32(fact, lw->inv_weight);

	fact_hi = (u32)(fact >> 32);
	if (fact_hi) {
		fs = fls(fact_hi);
		shift -= fs;
		fact >>= fs;
	}

	return mul_u64_u32_shr(delta_exec, fact, shift);
}

/*
 * delta /= w
 */
static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
{
	if (unlikely(se->load.weight != NICE_0_LOAD))
		delta = __calc_delta(delta, NICE_0_LOAD, &se->load);

	return delta;
}

const struct sched_class fair_sched_class;

/**************************************************************
 * CFS operations on generic schedulable entities:
 */

#ifdef CONFIG_FAIR_GROUP_SCHED

/* Walk up scheduling entities hierarchy */
#define for_each_sched_entity(se) \
		for (; se; se = se->parent)

static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
	struct rq *rq = rq_of(cfs_rq);
	int cpu = cpu_of(rq);

	if (cfs_rq->on_list)
		return rq->tmp_alone_branch == &rq->leaf_cfs_rq_list;

	cfs_rq->on_list = 1;

	/*
	 * Ensure we either appear before our parent (if already
	 * enqueued) or force our parent to appear after us when it is
	 * enqueued. The fact that we always enqueue bottom-up
	 * reduces this to two cases and a special case for the root
	 * cfs_rq. Furthermore, it also means that we will always reset
	 * tmp_alone_branch either when the branch is connected
	 * to a tree or when we reach the top of the tree
	 */
	if (cfs_rq->tg->parent &&
	    cfs_rq->tg->parent->cfs_rq[cpu]->on_list) {
		/*
		 * If parent is already on the list, we add the child
		 * just before. Thanks to circular linked property of
		 * the list, this means to put the child at the tail
		 * of the list that starts by parent.
		 */
		list_add_tail_rcu(&cfs_rq->leaf_cfs_rq_list,
			&(cfs_rq->tg->parent->cfs_rq[cpu]->leaf_cfs_rq_list));
		/*
		 * The branch is now connected to its tree so we can
		 * reset tmp_alone_branch to the beginning of the
		 * list.
		 */
		rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
		return true;
	}

	if (!cfs_rq->tg->parent) {
		/*
		 * cfs rq without parent should be put
		 * at the tail of the list.
		 */
		list_add_tail_rcu(&cfs_rq->leaf_cfs_rq_list,
			&rq->leaf_cfs_rq_list);
		/*
		 * We have reach the top of a tree so we can reset
		 * tmp_alone_branch to the beginning of the list.
		 */
		rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
		return true;
	}

	/*
	 * The parent has not already been added so we want to
	 * make sure that it will be put after us.
	 * tmp_alone_branch points to the begin of the branch
	 * where we will add parent.
	 */
	list_add_rcu(&cfs_rq->leaf_cfs_rq_list, rq->tmp_alone_branch);
	/*
	 * update tmp_alone_branch to points to the new begin
	 * of the branch
	 */
	rq->tmp_alone_branch = &cfs_rq->leaf_cfs_rq_list;
	return false;
}

static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
	if (cfs_rq->on_list) {
		struct rq *rq = rq_of(cfs_rq);

		/*
		 * With cfs_rq being unthrottled/throttled during an enqueue,
		 * it can happen the tmp_alone_branch points to the leaf that
		 * we finally want to delete. In this case, tmp_alone_branch moves
		 * to the prev element but it will point to rq->leaf_cfs_rq_list
		 * at the end of the enqueue.
		 */
		if (rq->tmp_alone_branch == &cfs_rq->leaf_cfs_rq_list)
			rq->tmp_alone_branch = cfs_rq->leaf_cfs_rq_list.prev;

		list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
		cfs_rq->on_list = 0;
	}
}

static inline void assert_list_leaf_cfs_rq(struct rq *rq)
{
	SCHED_WARN_ON(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list);
}

/* Iterate through all leaf cfs_rq's on a runqueue */
#define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos)			\
	list_for_each_entry_safe(cfs_rq, pos, &rq->leaf_cfs_rq_list,	\
				 leaf_cfs_rq_list)

/* Do the two (enqueued) entities belong to the same group ? */
static inline struct cfs_rq *
is_same_group(struct sched_entity *se, struct sched_entity *pse)
{
	if (se->cfs_rq == pse->cfs_rq)
		return se->cfs_rq;

	return NULL;
}

static inline struct sched_entity *parent_entity(const struct sched_entity *se)
{
	return se->parent;
}

static void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
	int se_depth, pse_depth;

	/*
	 * preemption test can be made between sibling entities who are in the
	 * same cfs_rq i.e who have a common parent. Walk up the hierarchy of
	 * both tasks until we find their ancestors who are siblings of common
	 * parent.
	 */

	/* First walk up until both entities are at same depth */
	se_depth = (*se)->depth;
	pse_depth = (*pse)->depth;

	while (se_depth > pse_depth) {
		se_depth--;
		*se = parent_entity(*se);
	}

	while (pse_depth > se_depth) {
		pse_depth--;
		*pse = parent_entity(*pse);
	}

	while (!is_same_group(*se, *pse)) {
		*se = parent_entity(*se);
		*pse = parent_entity(*pse);
	}
}

static int tg_is_idle(struct task_group *tg)
{
	return tg->idle > 0;
}

static int cfs_rq_is_idle(struct cfs_rq *cfs_rq)
{
	return cfs_rq->idle > 0;
}

static int se_is_idle(struct sched_entity *se)
{
	if (entity_is_task(se))
		return task_has_idle_policy(task_of(se));
	return cfs_rq_is_idle(group_cfs_rq(se));
}

#else	/* !CONFIG_FAIR_GROUP_SCHED */

#define for_each_sched_entity(se) \
		for (; se; se = NULL)

static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
	return true;
}

static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
}

static inline void assert_list_leaf_cfs_rq(struct rq *rq)
{
}

#define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos)	\
		for (cfs_rq = &rq->cfs, pos = NULL; cfs_rq; cfs_rq = pos)

static inline struct sched_entity *parent_entity(struct sched_entity *se)
{
	return NULL;
}

static inline void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
}

static inline int tg_is_idle(struct task_group *tg)
{
	return 0;
}

static int cfs_rq_is_idle(struct cfs_rq *cfs_rq)
{
	return 0;
}

static int se_is_idle(struct sched_entity *se)
{
	return 0;
}

#endif	/* CONFIG_FAIR_GROUP_SCHED */

static __always_inline
void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec);

/**************************************************************
 * Scheduling class tree data structure manipulation methods:
 */

static inline u64 max_vruntime(u64 max_vruntime, u64 vruntime)
{
	s64 delta = (s64)(vruntime - max_vruntime);
	if (delta > 0)
		max_vruntime = vruntime;

	return max_vruntime;
}

static inline u64 min_vruntime(u64 min_vruntime, u64 vruntime)
{
	s64 delta = (s64)(vruntime - min_vruntime);
	if (delta < 0)
		min_vruntime = vruntime;

	return min_vruntime;
}

static inline bool entity_before(const struct sched_entity *a,
				 const struct sched_entity *b)
{
	/*
	 * Tiebreak on vruntime seems unnecessary since it can
	 * hardly happen.
	 */
	return (s64)(a->deadline - b->deadline) < 0;
}

static inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	return (s64)(se->vruntime - cfs_rq->min_vruntime);
}

#define __node_2_se(node) \
	rb_entry((node), struct sched_entity, run_node)

/*
 * Compute virtual time from the per-task service numbers:
 *
 * Fair schedulers conserve lag:
 *
 *   \Sum lag_i = 0
 *
 * Where lag_i is given by:
 *
 *   lag_i = S - s_i = w_i * (V - v_i)
 *
 * Where S is the ideal service time and V is it's virtual time counterpart.
 * Therefore:
 *
 *   \Sum lag_i = 0
 *   \Sum w_i * (V - v_i) = 0
 *   \Sum w_i * V - w_i * v_i = 0
 *
 * From which we can solve an expression for V in v_i (which we have in
 * se->vruntime):
 *
 *       \Sum v_i * w_i   \Sum v_i * w_i
 *   V = -------------- = --------------
 *          \Sum w_i            W
 *
 * Specifically, this is the weighted average of all entity virtual runtimes.
 *
 * [[ NOTE: this is only equal to the ideal scheduler under the condition
 *          that join/leave operations happen at lag_i = 0, otherwise the
 *          virtual time has non-contiguous motion equivalent to:
 *
 *	      V +-= lag_i / W
 *
 *	    Also see the comment in place_entity() that deals with this. ]]
 *
 * However, since v_i is u64, and the multiplication could easily overflow
 * transform it into a relative form that uses smaller quantities:
 *
 * Substitute: v_i == (v_i - v0) + v0
 *
 *     \Sum ((v_i - v0) + v0) * w_i   \Sum (v_i - v0) * w_i
 * V = ---------------------------- = --------------------- + v0
 *                  W                            W
 *
 * Which we track using:
 *
 *                    v0 := cfs_rq->min_vruntime
 * \Sum (v_i - v0) * w_i := cfs_rq->avg_vruntime
 *              \Sum w_i := cfs_rq->avg_load
 *
 * Since min_vruntime is a monotonic increasing variable that closely tracks
 * the per-task service, these deltas: (v_i - v), will be in the order of the
 * maximal (virtual) lag induced in the system due to quantisation.
 *
 * Also, we use scale_load_down() to reduce the size.
 *
 * As measured, the max (key * weight) value was ~44 bits for a kernel build.
 */
static void
avg_vruntime_add(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	unsigned long weight = scale_load_down(se->load.weight);
	s64 key = entity_key(cfs_rq, se);

	cfs_rq->avg_vruntime += key * weight;
	cfs_rq->avg_load += weight;
}

static void
avg_vruntime_sub(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	unsigned long weight = scale_load_down(se->load.weight);
	s64 key = entity_key(cfs_rq, se);

	cfs_rq->avg_vruntime -= key * weight;
	cfs_rq->avg_load -= weight;
}

static inline
void avg_vruntime_update(struct cfs_rq *cfs_rq, s64 delta)
{
	/*
	 * v' = v + d ==> avg_vruntime' = avg_runtime - d*avg_load
	 */
	cfs_rq->avg_vruntime -= cfs_rq->avg_load * delta;
}

/*
 * Specifically: avg_runtime() + 0 must result in entity_eligible() := true
 * For this to be so, the result of this function must have a left bias.
 */
u64 avg_vruntime(struct cfs_rq *cfs_rq)
{
	struct sched_entity *curr = cfs_rq->curr;
	s64 avg = cfs_rq->avg_vruntime;
	long load = cfs_rq->avg_load;

	if (curr && curr->on_rq) {
		unsigned long weight = scale_load_down(curr->load.weight);

		avg += entity_key(cfs_rq, curr) * weight;
		load += weight;
	}

	if (load) {
		/* sign flips effective floor / ceiling */
		if (avg < 0)
			avg -= (load - 1);
		avg = div_s64(avg, load);
	}

	return cfs_rq->min_vruntime + avg;
}

/*
 * lag_i = S - s_i = w_i * (V - v_i)
 *
 * However, since V is approximated by the weighted average of all entities it
 * is possible -- by addition/removal/reweight to the tree -- to move V around
 * and end up with a larger lag than we started with.
 *
 * Limit this to either double the slice length with a minimum of TICK_NSEC
 * since that is the timing granularity.
 *
 * EEVDF gives the following limit for a steady state system:
 *
 *   -r_max < lag < max(r_max, q)
 *
 * XXX could add max_slice to the augmented data to track this.
 */
static s64 entity_lag(u64 avruntime, struct sched_entity *se)
{
	s64 vlag, limit;

	vlag = avruntime - se->vruntime;
	limit = calc_delta_fair(max_t(u64, 2*se->slice, TICK_NSEC), se);

	return clamp(vlag, -limit, limit);
}

static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	SCHED_WARN_ON(!se->on_rq);

	se->vlag = entity_lag(avg_vruntime(cfs_rq), se);
}

/*
 * Entity is eligible once it received less service than it ought to have,
 * eg. lag >= 0.
 *
 * lag_i = S - s_i = w_i*(V - v_i)
 *
 * lag_i >= 0 -> V >= v_i
 *
 *     \Sum (v_i - v)*w_i
 * V = ------------------ + v
 *          \Sum w_i
 *
 * lag_i >= 0 -> \Sum (v_i - v)*w_i >= (v_i - v)*(\Sum w_i)
 *
 * Note: using 'avg_vruntime() > se->vruntime' is inaccurate due
 *       to the loss in precision caused by the division.
 */
static int vruntime_eligible(struct cfs_rq *cfs_rq, u64 vruntime)
{
	struct sched_entity *curr = cfs_rq->curr;
	s64 avg = cfs_rq->avg_vruntime;
	long load = cfs_rq->avg_load;

	if (curr && curr->on_rq) {
		unsigned long weight = scale_load_down(curr->load.weight);

		avg += entity_key(cfs_rq, curr) * weight;
		load += weight;
	}

	return avg >= (s64)(vruntime - cfs_rq->min_vruntime) * load;
}

int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	return vruntime_eligible(cfs_rq, se->vruntime);
}

static u64 __update_min_vruntime(struct cfs_rq *cfs_rq, u64 vruntime)
{
	u64 min_vruntime = cfs_rq->min_vruntime;
	/*
	 * open coded max_vruntime() to allow updating avg_vruntime
	 */
	s64 delta = (s64)(vruntime - min_vruntime);
	if (delta > 0) {
		avg_vruntime_update(cfs_rq, delta);
		min_vruntime = vruntime;
	}
	return min_vruntime;
}

static void update_min_vruntime(struct cfs_rq *cfs_rq)
{
	struct sched_entity *se = __pick_root_entity(cfs_rq);
	struct sched_entity *curr = cfs_rq->curr;
	u64 vruntime = cfs_rq->min_vruntime;

	if (curr) {
		if (curr->on_rq)
			vruntime = curr->vruntime;
		else
			curr = NULL;
	}

	if (se) {
		if (!curr)
			vruntime = se->min_vruntime;
		else
			vruntime = min_vruntime(vruntime, se->min_vruntime);
	}

	/* ensure we never gain time by being placed backwards. */
	u64_u32_store(cfs_rq->min_vruntime,
		      __update_min_vruntime(cfs_rq, vruntime));
}

static inline bool __entity_less(struct rb_node *a, const struct rb_node *b)
{
	return entity_before(__node_2_se(a), __node_2_se(b));
}

#define vruntime_gt(field, lse, rse) ({ (s64)((lse)->field - (rse)->field) > 0; })

static inline void __min_vruntime_update(struct sched_entity *se, struct rb_node *node)
{
	if (node) {
		struct sched_entity *rse = __node_2_se(node);
		if (vruntime_gt(min_vruntime, se, rse))
			se->min_vruntime = rse->min_vruntime;
	}
}

/*
 * se->min_vruntime = min(se->vruntime, {left,right}->min_vruntime)
 */
static inline bool min_vruntime_update(struct sched_entity *se, bool exit)
{
	u64 old_min_vruntime = se->min_vruntime;
	struct rb_node *node = &se->run_node;

	se->min_vruntime = se->vruntime;
	__min_vruntime_update(se, node->rb_right);
	__min_vruntime_update(se, node->rb_left);

	return se->min_vruntime == old_min_vruntime;
}

RB_DECLARE_CALLBACKS(static, min_vruntime_cb, struct sched_entity,
		     run_node, min_vruntime, min_vruntime_update);

/*
 * Enqueue an entity into the rb-tree:
 */
static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	avg_vruntime_add(cfs_rq, se);
	se->min_vruntime = se->vruntime;
	rb_add_augmented_cached(&se->run_node, &cfs_rq->tasks_timeline,
				__entity_less, &min_vruntime_cb);
}

static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	rb_erase_augmented_cached(&se->run_node, &cfs_rq->tasks_timeline,
				  &min_vruntime_cb);
	avg_vruntime_sub(cfs_rq, se);
}

struct sched_entity *__pick_root_entity(struct cfs_rq *cfs_rq)
{
	struct rb_node *root = cfs_rq->tasks_timeline.rb_root.rb_node;

	if (!root)
		return NULL;

	return __node_2_se(root);
}

struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
{
	struct rb_node *left = rb_first_cached(&cfs_rq->tasks_timeline);

	if (!left)
		return NULL;

	return __node_2_se(left);
}

/*
 * Earliest Eligible Virtual Deadline First
 *
 * In order to provide latency guarantees for different request sizes
 * EEVDF selects the best runnable task from two criteria:
 *
 *  1) the task must be eligible (must be owed service)
 *
 *  2) from those tasks that meet 1), we select the one
 *     with the earliest virtual deadline.
 *
 * We can do this in O(log n) time due to an augmented RB-tree. The
 * tree keeps the entries sorted on deadline, but also functions as a
 * heap based on the vruntime by keeping:
 *
 *  se->min_vruntime = min(se->vruntime, se->{left,right}->min_vruntime)
 *
 * Which allows tree pruning through eligibility.
 */
static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq)
{
	struct rb_node *node = cfs_rq->tasks_timeline.rb_root.rb_node;
	struct sched_entity *se = __pick_first_entity(cfs_rq);
	struct sched_entity *curr = cfs_rq->curr;
	struct sched_entity *best = NULL;

	/*
	 * We can safely skip eligibility check if there is only one entity
	 * in this cfs_rq, saving some cycles.
	 */
	if (cfs_rq->nr_running == 1)
		return curr && curr->on_rq ? curr : se;

	if (curr && (!curr->on_rq || !entity_eligible(cfs_rq, curr)))
		curr = NULL;

	/*
	 * Once selected, run a task until it either becomes non-eligible or
	 * until it gets a new slice. See the HACK in set_next_entity().
	 */
	if (sched_feat(RUN_TO_PARITY) && curr && curr->vlag == curr->deadline)
		return curr;

	/* Pick the leftmost entity if it's eligible */
	if (se && entity_eligible(cfs_rq, se)) {
		best = se;
		goto found;
	}

	/* Heap search for the EEVD entity */
	while (node) {
		struct rb_node *left = node->rb_left;

		/*
		 * Eligible entities in left subtree are always better
		 * choices, since they have earlier deadlines.
		 */
		if (left && vruntime_eligible(cfs_rq,
					__node_2_se(left)->min_vruntime)) {
			node = left;
			continue;
		}

		se = __node_2_se(node);

		/*
		 * The left subtree either is empty or has no eligible
		 * entity, so check the current node since it is the one
		 * with earliest deadline that might be eligible.
		 */
		if (entity_eligible(cfs_rq, se)) {
			best = se;
			break;
		}

		node = node->rb_right;
	}
found:
	if (!best || (curr && entity_before(curr, best)))
		best = curr;

	return best;
}

#ifdef CONFIG_SCHED_DEBUG
struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
{
	struct rb_node *last = rb_last(&cfs_rq->tasks_timeline.rb_root);

	if (!last)
		return NULL;

	return __node_2_se(last);
}

/**************************************************************
 * Scheduling class statistics methods:
 */
#ifdef CONFIG_SMP
int sched_update_scaling(void)
{
	unsigned int factor = get_update_sysctl_factor();

#define WRT_SYSCTL(name) \
	(normalized_sysctl_##name = sysctl_##name / (factor))
	WRT_SYSCTL(sched_base_slice);
#undef WRT_SYSCTL

	return 0;
}
#endif
#endif

static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se);

/*
 * XXX: strictly: vd_i += N*r_i/w_i such that: vd_i > ve_i
 * this is probably good enough.
 */
static void update_deadline(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	if ((s64)(se->vruntime - se->deadline) < 0)
		return;

	/*
	 * For EEVDF the virtual time slope is determined by w_i (iow.
	 * nice) while the request time r_i is determined by
	 * sysctl_sched_base_slice.
	 */
	se->slice = sysctl_sched_base_slice;

	/*
	 * EEVDF: vd_i = ve_i + r_i / w_i
	 */
	se->deadline = se->vruntime + calc_delta_fair(se->slice, se);

	/*
	 * The task has consumed its request, reschedule.
	 */
	if (cfs_rq->nr_running > 1) {
		resched_curr(rq_of(cfs_rq));
		clear_buddies(cfs_rq, se);
	}
}

#include "pelt.h"
#ifdef CONFIG_SMP

static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu);
static unsigned long task_h_load(struct task_struct *p);
static unsigned long capacity_of(int cpu);

/* Give new sched_entity start runnable values to heavy its load in infant time */
void init_entity_runnable_average(struct sched_entity *se)
{
	struct sched_avg *sa = &se->avg;

	memset(sa, 0, sizeof(*sa));

	/*
	 * Tasks are initialized with full load to be seen as heavy tasks until
	 * they get a chance to stabilize to their real load level.
	 * Group entities are initialized with zero load to reflect the fact that
	 * nothing has been attached to the task group yet.
	 */
	if (entity_is_task(se))
		sa->load_avg = scale_load_down(se->load.weight);

	/* when this task is enqueued, it will contribute to its cfs_rq's load_avg */
}

/*
 * With new tasks being created, their initial util_avgs are extrapolated
 * based on the cfs_rq's current util_avg:
 *
 *   util_avg = cfs_rq->avg.util_avg / (cfs_rq->avg.load_avg + 1)
 *		* se_weight(se)
 *
 * However, in many cases, the above util_avg does not give a desired
 * value. Moreover, the sum of the util_avgs may be divergent, such
 * as when the series is a harmonic series.
 *
 * To solve this problem, we also cap the util_avg of successive tasks to
 * only 1/2 of the left utilization budget:
 *
 *   util_avg_cap = (cpu_scale - cfs_rq->avg.util_avg) / 2^n
 *
 * where n denotes the nth task and cpu_scale the CPU capacity.
 *
 * For example, for a CPU with 1024 of capacity, a simplest series from
 * the beginning would be like:
 *
 *  task  util_avg: 512, 256, 128,  64,  32,   16,    8, ...
 * cfs_rq util_avg: 512, 768, 896, 960, 992, 1008, 1016, ...
 *
 * Finally, that extrapolated util_avg is clamped to the cap (util_avg_cap)
 * if util_avg > util_avg_cap.
 */
void post_init_entity_util_avg(struct task_struct *p)
{
	struct sched_entity *se = &p->se;
	struct cfs_rq *cfs_rq = cfs_rq_of(se);
	struct sched_avg *sa = &se->avg;
	long cpu_scale = arch_scale_cpu_capacity(cpu_of(rq_of(cfs_rq)));
	long cap = (long)(cpu_scale - cfs_rq->avg.util_avg) / 2;

	if (p->sched_class != &fair_sched_class) {
		/*
		 * For !fair tasks do:
		 *
		update_cfs_rq_load_avg(now, cfs_rq);
		attach_entity_load_avg(cfs_rq, se);
		switched_from_fair(rq, p);
		 *
		 * such that the next switched_to_fair() has the
		 * expected state.
		 */
		se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq);
		return;
	}

	if (cap > 0) {
		if (cfs_rq->avg.util_avg != 0) {
			sa->util_avg  = cfs_rq->avg.util_avg * se_weight(se);
			sa->util_avg /= (cfs_rq->avg.load_avg + 1);

			if (sa->util_avg > cap)
				sa->util_avg = cap;
		} else {
			sa->util_avg = cap;
		}
	}

	sa->runnable_avg = sa->util_avg;
}

#else /* !CONFIG_SMP */
void init_entity_runnable_average(struct sched_entity *se)
{
}
void post_init_entity_util_avg(struct task_struct *p)
{
}
static void update_tg_load_avg(struct cfs_rq *cfs_rq)
{
}
#endif /* CONFIG_SMP */

static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
{
	u64 now = rq_clock_task(rq);
	s64 delta_exec;

	delta_exec = now - curr->exec_start;
	if (unlikely(delta_exec <= 0))
		return delta_exec;

	curr->exec_start = now;
	curr->sum_exec_runtime += delta_exec;

	if (schedstat_enabled()) {
		struct sched_statistics *stats;

		stats = __schedstats_from_se(curr);
		__schedstat_set(stats->exec_max,
				max(delta_exec, stats->exec_max));
	}

	return delta_exec;
}

static inline void update_curr_task(struct task_struct *p, s64 delta_exec)
{
	trace_sched_stat_runtime(p, delta_exec);
	account_group_exec_runtime(p, delta_exec);
	cgroup_account_cputime(p, delta_exec);
	if (p->dl_server)
		dl_server_update(p->dl_server, delta_exec);
}

/*
 * Used by other classes to account runtime.
 */
s64 update_curr_common(struct rq *rq)
{
	struct task_struct *curr = rq->curr;
	s64 delta_exec;

	delta_exec = update_curr_se(rq, &curr->se);
	if (likely(delta_exec > 0))
		update_curr_task(curr, delta_exec);

	return delta_exec;
}

/*
 * Update the current task's runtime statistics.
 */
static void update_curr(struct cfs_rq *cfs_rq)
{
	struct sched_entity *curr = cfs_rq->curr;
	s64 delta_exec;

	if (unlikely(!curr))
		return;

	delta_exec = update_curr_se(rq_of(cfs_rq), curr);
	if (unlikely(delta_exec <= 0))
		return;

	curr->vruntime += calc_delta_fair(delta_exec, curr);
	update_deadline(cfs_rq, curr);
	update_min_vruntime(cfs_rq);

	if (entity_is_task(curr))
		update_curr_task(task_of(curr), delta_exec);

	account_cfs_rq_runtime(cfs_rq, delta_exec);
}

static void update_curr_fair(struct rq *rq)
{
	update_curr(cfs_rq_of(&rq->curr->se));
}

static inline void
update_stats_wait_start_fair(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	struct sched_statistics *stats;
	struct task_struct *p = NULL;

	if (!schedstat_enabled())
		return;

	stats = __schedstats_from_se(se);

	if (entity_is_task(se))
		p = task_of(se);

	__update_stats_wait_start(rq_of(cfs_rq), p, stats);
}

static inline void
update_stats_wait_end_fair(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	struct sched_statistics *stats;
	struct task_struct *p = NULL;

	if (!schedstat_enabled())
		return;

	stats = __schedstats_from_se(se);

	/*
	 * When the sched_schedstat changes from 0 to 1, some sched se
	 * maybe already in the runqueue, the se->statistics.wait_start
	 * will be 0.So it will let the delta wrong. We need to avoid this
	 * scenario.
	 */
	if (unlikely(!schedstat_val(stats->wait_start)))
		return;

	if (entity_is_task(se))
		p = task_of(se);

	__update_stats_wait_end(rq_of(cfs_rq), p, stats);
}

static inline void
update_stats_enqueue_sleeper_fair(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	struct sched_statistics *stats;
	struct task_struct *tsk = NULL;

	if (!schedstat_enabled())
		return;

	stats = __schedstats_from_se(se);

	if (entity_is_task(se))
		tsk = task_of(se);

	__update_stats_enqueue_sleeper(rq_of(cfs_rq), tsk, stats);
}

/*
 * Task is being enqueued - update stats:
 */
static inline void
update_stats_enqueue_fair(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
	if (!schedstat_enabled())
		return;

	/*
	 * Are we enqueueing a waiting task? (for current tasks
	 * a dequeue/enqueue event is a NOP)
	 */
	if (se != cfs_rq->curr)
		update_stats_wait_start_fair(cfs_rq, se);

	if (flags & ENQUEUE_WAKEUP)
		update_stats_enqueue_sleeper_fair(cfs_rq, se);
}

static inline void
update_stats_dequeue_fair(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{

	if (!schedstat_enabled())
		return;

	/*
	 * Mark the end of the wait period if dequeueing a
	 * waiting task:
	 */
	if (se != cfs_rq->curr)
		update_stats_wait_end_fair(cfs_rq, se);

	if ((flags & DEQUEUE_SLEEP) && entity_is_task(se)) {
		struct task_struct *tsk = task_of(se);
		unsigned int state;

		/* XXX racy against TTWU */
		state = READ_ONCE(tsk->__state);
		if (state & TASK_INTERRUPTIBLE)
			__schedstat_set(tsk->stats.sleep_start,
				      rq_clock(rq_of(cfs_rq)));
		if (state & TASK_UNINTERRUPTIBLE)
			__schedstat_set(tsk->stats.block_start,
				      rq_clock(rq_of(cfs_rq)));
	}
}

/*
 * We are picking a new current task - update its stats:
 */
static inline void
update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
	/*
	 * We are starting a new run period:
	 */
	se->exec_start = rq_clock_task(rq_of(cfs_rq));
}

/**************************************************
 * Scheduling class queueing methods:
 */

static inline bool is_core_idle(int cpu)
{
#ifdef CONFIG_SCHED_SMT
	int sibling;

	for_each_cpu(sibling, cpu_smt_mask(cpu)) {
		if (cpu == sibling)
			continue;

		if (!idle_cpu(sibling))
			return false;
	}
#endif

	return true;
}

#ifdef CONFIG_NUMA
#define NUMA_IMBALANCE_MIN 2

static inline long
adjust_numa_imbalance(int imbalance, int dst_running, int imb_numa_nr)
{
	/*
	 * Allow a NUMA imbalance if busy CPUs is less than the maximum
	 * threshold. Above this threshold, individual tasks may be contending
	 * for both memory bandwidth and any shared HT resources.  This is an
	 * approximation as the number of running tasks may not be related to
	 * the number of busy CPUs due to sched_setaffinity.
	 */
	if (dst_running > imb_numa_nr)
		return imbalance;

	/*
	 * Allow a small imbalance based on a simple pair of communicating
	 * tasks that remain local when the destination is lightly loaded.
	 */
	if (imbalance <= NUMA_IMBALANCE_MIN)
		return 0;

	return imbalance;
}
#endif /* CONFIG_NUMA */

#ifdef CONFIG_NUMA_BALANCING
/*
 * Approximate time to scan a full NUMA task in ms. The task scan period is
 * calculated based on the tasks virtual memory size and
 * numa_balancing_scan_size.
 */
unsigned int sysctl_numa_balancing_scan_period_min = 1000;
unsigned int sysctl_numa_balancing_scan_period_max = 60000;

/* Portion of address space to scan in MB */
unsigned int sysctl_numa_balancing_scan_size = 256;

/* Scan @scan_size MB every @scan_period after an initial @scan_delay in ms */
unsigned int sysctl_numa_balancing_scan_delay = 1000;

/* The page with hint page fault latency < threshold in ms is considered hot */
unsigned int sysctl_numa_balancing_hot_threshold = MSEC_PER_SEC;

struct numa_group {
	refcount_t refcount;

	spinlock_t lock; /* nr_tasks, tasks */
	int nr_tasks;
	pid_t gid;
	int active_nodes;

	struct rcu_head rcu;
	unsigned long total_faults;
	unsigned long max_faults_cpu;
	/*
	 * faults[] array is split into two regions: faults_mem and faults_cpu.
	 *
	 * Faults_cpu is used to decide whether memory should move
	 * towards the CPU. As a consequence, these stats are weighted
	 * more by CPU use than by memory faults.
	 */
	unsigned long faults[];
};

/*
 * For functions that can be called in multiple contexts that permit reading
 * ->numa_group (see struct task_struct for locking rules).
 */
static struct numa_group *deref_task_numa_group(struct task_struct *p)
{
	return rcu_dereference_check(p->numa_group, p == current ||
		(lockdep_is_held(__rq_lockp(task_rq(p))) && !READ_ONCE(p->on_cpu)));
}

static struct numa_group *deref_curr_numa_group(struct task_struct *p)
{
	return rcu_dereference_protected(p->numa_group, p == current);
}

static inline unsigned long group_faults_priv(struct numa_group *ng);
static inline unsigned long group_faults_shared(struct numa_group *ng);

static unsigned int task_nr_scan_windows(struct task_struct *p)
{
	unsigned long rss = 0;
	unsigned long nr_scan_pages;

	/*
	 * Calculations based on RSS as non-present and empty pages are skipped
	 * by the PTE scanner and NUMA hinting faults should be trapped based
	 * on resident pages
	 */
	nr_scan_pages = sysctl_numa_balancing_scan_size << (20 - PAGE_SHIFT);
	rss = get_mm_rss(p->mm);
	if (!rss)
		rss = nr_scan_pages;

	rss = round_up(rss, nr_scan_pages);
	return rss / nr_scan_pages;
}

/* For sanity's sake, never scan more PTEs than MAX_SCAN_WINDOW MB/sec. */
#define MAX_SCAN_WINDOW 2560

static unsigned int task_scan_min(struct task_struct *p)
{
	unsigned int scan_size = READ_ONCE(sysctl_numa_balancing_scan_size);
	unsigned int scan, floor;
	unsigned int windows = 1;

	if (scan_size < MAX_SCAN_WINDOW)
		windows = MAX_SCAN_WINDOW / scan_size;
	floor = 1000 / windows;

	scan = sysctl_numa_balancing_scan_period_min / task_nr_scan_windows(p);
	return max_t(unsigned int, floor, scan);
}

static unsigned int task_scan_start(struct task_struct *p)
{
	unsigned long smin = task_scan_min(p);
	unsigned long period = smin;
	struct numa_group *ng;

	/* Scale the maximum scan period with the amount of shared memory. */
	rcu_read_lock();
	ng = rcu_dereference(p->numa_group);
	if (ng) {
		unsigned long shared = group_faults_shared(ng);
		unsigned long private = group_faults_priv(ng);

		period *= refcount_read(&ng->refcount);
		period *= shared + 1;
		period /= private + shared + 1;
	}
	rcu_read_unlock();

	return max(smin, period);
}

static unsigned int task_scan_max(struct task_struct *p)
{
	unsigned long smin = task_scan_min(p);
	unsigned long smax;
	struct numa_group *ng;

	/* Watch for min being lower than max due to floor calculations */
	smax = sysctl_numa_balancing_scan_period_max / task_nr_scan_windows(p);

	/* Scale the maximum scan period with the amount of shared memory. */
	ng = deref_curr_numa_group(p);
	if (ng) {
		unsigned long shared = group_faults_shared(ng);
		unsigned long private = group_faults_priv(ng);
		unsigned long period = smax;

		period *= refcount_read(&ng->refcount);
		period *= shared + 1;
		period /= private + shared + 1;

		smax = max(smax, period);
	}

	return max(smin, smax);
}

static void account_numa_enqueue(struct rq *rq, struct task_struct *p)
{
	rq->nr_numa_running += (p->numa_preferred_nid != NUMA_NO_NODE);
	rq->nr_preferred_running += (p->numa_preferred_nid == task_node(p));
}

static void account_numa_dequeue(struct rq *rq, struct task_struct *p)
{
	rq->nr_numa_running -= (p->numa_preferred_nid != NUMA_NO_NODE);
	rq->nr_preferred_running -= (p->numa_preferred_nid == task_node(p));
}

/* Shared or private faults. */
#define NR_NUMA_HINT_FAULT_TYPES 2

/* Memory and CPU locality */
#define NR_NUMA_HINT_FAULT_STATS (NR_NUMA_HINT_FAULT_TYPES * 2)

/* Averaged statistics, and temporary buffers. */
#define NR_NUMA_HINT_FAULT_BUCKETS (NR_NUMA_HINT_FAULT_STATS * 2)

pid_t task_numa_group_id(struct task_struct *p)
{
	struct numa_group *ng;
	pid_t gid = 0;

	rcu_read_lock();
	ng = rcu_dereference(p->numa_group);
	if (ng)
		gid = ng->gid;
	rcu_read_unlock();

	return gid;
}

/*
 * The averaged statistics, shared & private, memory & CPU,
 * occupy the first half of the array. The second half of the
 * array is for current counters, which are averaged into the
 * first set by task_numa_placement.
 */
static inline int task_faults_idx(enum numa_faults_stats s, int nid, int priv)
{
	return NR_NUMA_HINT_FAULT_TYPES * (s * nr_node_ids + nid) + priv;
}

static inline unsigned long task_faults(struct task_struct *p, int nid)
{
	if (!p->numa_faults)
		return 0;

	return p->numa_faults[task_faults_idx(NUMA_MEM, nid, 0)] +
		p->numa_faults[task_faults_idx(NUMA_MEM, nid, 1)];
}

static inline unsigned long group_faults(struct task_struct *p, int nid)
{
	struct numa_group *ng = deref_task_numa_group(p);

	if (!ng)
		return 0;

	return ng->faults[task_faults_idx(NUMA_MEM, nid, 0)] +
		ng->faults[task_faults_idx(NUMA_MEM, nid, 1)];
}

static inline unsigned long group_faults_cpu(struct numa_group *group, int nid)
{
	return group->faults[task_faults_idx(NUMA_CPU, nid, 0)] +
		group->faults[task_faults_idx(NUMA_CPU, nid, 1)];
}

static inline unsigned long group_faults_priv(struct numa_group *ng)
{
	unsigned long faults = 0;
	int node;

	for_each_online_node(node) {
		faults += ng->faults[task_faults_idx(NUMA_MEM, node, 1)];
	}

	return faults;
}

static inline unsigned long group_faults_shared(struct numa_group *ng)
{
	unsigned long faults = 0;
	int node;

	for_each_online_node(node) {
		faults += ng->faults[task_faults_idx(NUMA_MEM, node, 0)];
	}

	return faults;
}

/*
 * A node triggering more than 1/3 as many NUMA faults as the maximum is
 * considered part of a numa group's pseudo-interleaving set. Migrations
 * between these nodes are slowed down, to allow things to settle down.
 */
#define ACTIVE_NODE_FRACTION 3

static bool numa_is_active_node(int nid, struct numa_group *ng)
{
	return group_faults_cpu(ng, nid) * ACTIVE_NODE_FRACTION > ng->max_faults_cpu;
}

/* Handle placement on systems where not all nodes are directly connected. */
static unsigned long score_nearby_nodes(struct task_struct *p, int nid,
					int lim_dist, bool task)
{
	unsigned long score = 0;
	int node, max_dist;

	/*
	 * All nodes are directly connected, and the same distance
	 * from each other. No need for fancy placement algorithms.
	 */
	if (sched_numa_topology_type == NUMA_DIRECT)
		return 0;

	/* sched_max_numa_distance may be changed in parallel. */
	max_dist = READ_ONCE(sched_max_numa_distance);
	/*
	 * This code is called for each node, introducing N^2 complexity,
	 * which should be OK given the number of nodes rarely exceeds 8.
	 */
	for_each_online_node(node) {
		unsigned long faults;
		int dist = node_distance(nid, node);

		/*
		 * The furthest away nodes in the system are not interesting
		 * for placement; nid was already counted.
		 */
		if (dist >= max_dist || node == nid)
			continue;

		/*
		 * On systems with a backplane NUMA topology, compare groups
		 * of nodes, and move tasks towards the group with the most
		 * memory accesses. When comparing two nodes at distance
		 * "hoplimit", only nodes closer by than "hoplimit" are part
		 * of each group. Skip other nodes.
		 */
		if (sched_numa_topology_type == NUMA_BACKPLANE && dist >= lim_dist)
			continue;

		/* Add up the faults from nearby nodes. */
		if (task)
			faults = task_faults(p, node);
		else
			faults = group_faults(p, node);

		/*
		 * On systems with a glueless mesh NUMA topology, there are
		 * no fixed "groups of nodes". Instead, nodes that are not
		 * directly connected bounce traffic through intermediate
		 * nodes; a numa_group can occupy any set of nodes.
		 * The further away a node is, the less the faults count.
		 * This seems to result in good task placement.
		 */
		if (sched_numa_topology_type == NUMA_GLUELESS_MESH) {
			faults *= (max_dist - dist);
			faults /= (max_dist - LOCAL_DISTANCE);
		}

		score += faults;
	}

	return score;
}

/*
 * These return the fraction of accesses done by a particular task, or
 * task group, on a particular numa node.  The group weight is given a
 * larger multiplier, in order to group tasks together that are almost
 * evenly spread out between numa nodes.
 */
static inline unsigned long task_weight(struct task_struct *p, int nid,
					int dist)
{
	unsigned long faults, total_faults;

	if (!p->numa_faults)
		return 0;

	total_faults = p->total_numa_faults;

	if (!total_faults)
		return 0;

	faults = task_faults(p, nid);
	faults += score_nearby_nodes(p, nid, dist, true);

	return 1000 * faults / total_faults;
}

static inline unsigned long group_weight(struct task_struct *p, int nid,
					 int dist)
{
	struct numa_group *ng = deref_task_numa_group(p);
	unsigned long faults, total_faults;

	if (!ng)
		return 0;

	total_faults = ng->total_faults;

	if (!total_faults)
		return 0;

	faults = group_faults(p, nid);
	faults += score_nearby_nodes(p, nid, dist, false);

	return 1000 * faults / total_faults;
}

/*
 * If memory tiering mode is enabled, cpupid of slow memory page is
 * used to record scan time instead of CPU and PID.  When tiering mode
 * is disabled at run time, the scan time (in cpupid) will be
 * interpreted as CPU and PID.  So CPU needs to be checked to avoid to
 * access out of array bound.
 */
static inline bool cpupid_valid(int cpupid)
{
	return cpupid_to_cpu(cpupid) < nr_cpu_ids;
}

/*
 * For memory tiering mode, if there are enough free pages (more than
 * enough watermark defined here) in fast memory node, to take full
 * advantage of fast memory capacity, all recently accessed slow
 * memory pages will be migrated to fast memory node without
 * considering hot threshold.
 */
static bool pgdat_free_space_enough(struct pglist_data *pgdat)
{
	int z;
	unsigned long enough_wmark;

	enough_wmark = max(1UL * 1024 * 1024 * 1024 >> PAGE_SHIFT,
			   pgdat->node_present_pages >> 4);
	for (z = pgdat->nr_zones - 1; z >= 0; z--) {
		struct zone *zone = pgdat->node_zones + z;

		if (!populated_zone(zone))
			continue;

		if (zone_watermark_ok(zone, 0,
				      wmark_pages(zone, WMARK_PROMO) + enough_wmark,
				      ZONE_MOVABLE, 0))
			return true;
	}
	return false;
}

/*
 * For memory tiering mode, when page tables are scanned, the scan
 * time will be recorded in struct page in addition to make page
 * PROT_NONE for slow memory page.  So when the page is accessed, in
 * hint page fault handler, the hint page fault latency is calculated
 * via,
 *
 *	hint page fault latency = hint page fault time - scan time
 *
 * The smaller the hint page fault latency, the higher the possibility
 * for the page to be hot.
 */
static int numa_hint_fault_latency(struct folio *folio)
{
	int last_time, time;

	time = jiffies_to_msecs(jiffies);
	last_time = folio_xchg_access_time(folio, time);

	return (time - last_time) & PAGE_ACCESS_TIME_MASK;
}

/*
 * For memory tiering mode, too high promotion/demotion throughput may
 * hurt application latency.  So we provide a mechanism to rate limit
 * the number of pages that are tried to be promoted.
 */
static bool numa_promotion_rate_limit(struct pglist_data *pgdat,
				      unsigned long rate_limit, int nr)
{
	unsigned long nr_cand;
	unsigned int now, start;

	now = jiffies_to_msecs(jiffies);
	mod_node_page_state(pgdat, PGPROMOTE_CANDIDATE, nr);
	nr_cand = node_page_state(pgdat, PGPROMOTE_CANDIDATE);
	start = pgdat->nbp_rl_start;
	if (now - start > MSEC_PER_SEC &&
	    cmpxchg(&pgdat->nbp_rl_start, start, now) == start)
		pgdat->nbp_rl_nr_cand = nr_cand;
	if (nr_cand - pgdat->nbp_rl_nr_cand >= rate_limit)
		return true;
	return false;
}

#define NUMA_MIGRATION_ADJUST_STEPS	16

static void numa_promotion_adjust_threshold(struct pglist_data *pgdat,
					    unsigned long rate_limit,
					    unsigned int ref_th)
{
	unsigned int now, start, th_period, unit_th, th;
	unsigned long nr_cand, ref_cand, diff_cand;

	now = jiffies_to_msecs(jiffies);
	th_period = sysctl_numa_balancing_scan_period_max;
	start = pgdat->nbp_th_start;
	if (now - start > th_period &&
	    cmpxchg(&pgdat->nbp_th_start, start, now) == start) {
		ref_cand = rate_limit *
			sysctl_numa_balancing_scan_period_max / MSEC_PER_SEC;
		nr_cand = node_page_state(pgdat, PGPROMOTE_CANDIDATE);
		diff_cand = nr_cand - pgdat->nbp_th_nr_cand;
		unit_th = ref_th * 2 / NUMA_MIGRATION_ADJUST_STEPS;
		th = pgdat->nbp_threshold ? : ref_th;
		if (diff_cand > ref_cand * 11 / 10)
			th = max(th - unit_th, unit_th);
		else if (diff_cand < ref_cand * 9 / 10)
			th = min(th + unit_th, ref_th * 2);
		pgdat->nbp_th_nr_cand = nr_cand;
		pgdat->nbp_threshold = th;
	}
}

bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
				int src_nid, int dst_cpu)
{
	struct numa_group *ng = deref_curr_numa_group(p);
	int dst_nid = cpu_to_node(dst_cpu);
	int last_cpupid, this_cpupid;

	/*
	 * Cannot migrate to memoryless nodes.
	 */
	if (!node_state(dst_nid, N_MEMORY))
		return false;

	/*
	 * The pages in slow memory node should be migrated according
	 * to hot/cold instead of private/shared.
	 */
	if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING &&
	    !node_is_toptier(src_nid)) {
		struct pglist_data *pgdat;
		unsigned long rate_limit;
		unsigned int latency, th, def_th;

		pgdat = NODE_DATA(dst_nid);
		if (pgdat_free_space_enough(pgdat)) {
			/* workload changed, reset hot threshold */
			pgdat->nbp_threshold = 0;
			return true;
		}

		def_th = sysctl_numa_balancing_hot_threshold;
		rate_limit = sysctl_numa_balancing_promote_rate_limit << \
			(20 - PAGE_SHIFT);
		numa_promotion_adjust_threshold(pgdat, rate_limit, def_th);

		th = pgdat->nbp_threshold ? : def_th;
		latency = numa_hint_fault_latency(folio);
		if (latency >= th)
			return false;

		return !numa_promotion_rate_limit(pgdat, rate_limit,
						  folio_nr_pages(folio));
	}

	this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid);
	last_cpupid = folio_xchg_last_cpupid(folio, this_cpupid);

	if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) &&
	    !node_is_toptier(src_nid) && !cpupid_valid(last_cpupid))
		return false;

	/*
	 * Allow first faults or private faults to migrate immediately early in
	 * the lifetime of a task. The magic number 4 is based on waiting for
	 * two full passes of the "multi-stage node selection" test that is
	 * executed below.
	 */
	if ((p->numa_preferred_nid == NUMA_NO_NODE || p->numa_scan_seq <= 4) &&
	    (cpupid_pid_unset(last_cpupid) || cpupid_match_pid(p, last_cpupid)))
		return true;

	/*
	 * 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 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.
	 */
	if (!cpupid_pid_unset(last_cpupid) &&
				cpupid_to_nid(last_cpupid) != dst_nid)
		return false;

	/* Always allow migrate on private faults */
	if (cpupid_match_pid(p, last_cpupid))
		return true;

	/* A shared fault, but p->numa_group has not been set up yet. */
	if (!ng)
		return true;

	/*
	 * Destination node is much more heavily used than the source
	 * node? Allow migration.
	 */
	if (group_faults_cpu(ng, dst_nid) > group_faults_cpu(ng, src_nid) *
					ACTIVE_NODE_FRACTION)
		return true;

	/*
	 * Distribute memory according to CPU & memory use on each node,
	 * with 3/4 hysteresis to avoid unnecessary memory migrations:
	 *
	 * faults_cpu(dst)   3   faults_cpu(src)
	 * --------------- * - > ---------------
	 * faults_mem(dst)   4   faults_mem(src)
	 */
	return group_faults_cpu(ng, dst_nid) * group_faults(p, src_nid) * 3 >
	       group_faults_cpu(ng, src_nid) * group_faults(p, dst_nid) * 4;
}

/*
 * 'numa_type' describes the node at the moment of load balancing.
 */
enum numa_type {
	/* The node has spare capacity that can be used to run more tasks.  */
	node_has_spare = 0,
	/*
	 * The node is fully used and the tasks don't compete for more CPU
	 * cycles. Nevertheless, some tasks might wait before running.
	 */
	node_fully_busy,
	/*
	 * The node is overloaded and can't provide expected CPU cycles to all
	 * tasks.
	 */
	node_overloaded
};

/* Cached statistics for all CPUs within a node */
struct numa_stats {
	unsigned long load;
	unsigned long runnable;
	unsigned long util;
	/* Total compute capacity of CPUs on a node */
	unsigned long compute_capacity;
	unsigned int nr_running;
	unsigned int weight;
	enum numa_type node_type;
	int idle_cpu;
};

struct task_numa_env {
	struct task_struct *p;

	int src_cpu, src_nid;
	int dst_cpu, dst_nid;
	int imb_numa_nr;

	struct numa_stats src_stats, dst_stats;

	int imbalance_pct;
	int dist;

	struct task_struct *best_task;
	long best_imp;
	int best_cpu;
};

static unsigned long cpu_load(struct rq *rq);
static unsigned long cpu_runnable(struct rq *rq);

static inline enum
numa_type numa_classify(unsigned int imbalance_pct,
			 struct numa_stats *ns)
{
	if ((ns->nr_running > ns->weight) &&
	    (((ns->compute_capacity * 100) < (ns->util * imbalance_pct)) ||
	     ((ns->compute_capacity * imbalance_pct) < (ns->runnable * 100))))
		return node_overloaded;

	if ((ns->nr_running < ns->weight) ||
	    (((ns->compute_capacity * 100) > (ns->util * imbalance_pct)) &&
	     ((ns->compute_capacity * imbalance_pct) > (ns->runnable * 100))))
		return node_has_spare;

	return node_fully_busy;
}

#ifdef CONFIG_SCHED_SMT
/* Forward declarations of select_idle_sibling helpers */
static inline bool test_idle_cores(int cpu);
static inline int numa_idle_core(int idle_core, int cpu)
{
	if (!static_branch_likely(&sched_smt_present) ||
	    idle_core >= 0 || !test_idle_cores(cpu))
		return idle_core;

	/*
	 * Prefer cores instead of packing HT siblings
	 * and triggering future load balancing.
	 */
	if (is_core_idle(cpu))
		idle_core = cpu;

	return idle_core;
}
#else
static inline int numa_idle_core(int idle_core, int cpu)
{
	return idle_core;
}
#endif

/*
 * Gather all necessary information to make NUMA balancing placement
 * decisions that are compatible with standard load balancer. This
 * borrows code and logic from update_sg_lb_stats but sharing a
 * common implementation is impractical.
 */
static void update_numa_stats(struct task_numa_env *env,
			      struct numa_stats *ns, int nid,
			      bool find_idle)
{
	int cpu, idle_core = -1;

	memset(ns, 0, sizeof(*ns));
	ns->idle_cpu = -1;

	rcu_read_lock();
	for_each_cpu(cpu, cpumask_of_node(nid)) {
		struct rq *rq = cpu_rq(cpu);

		ns->load += cpu_load(rq);
		ns->runnable += cpu_runnable(rq);
		ns->util += cpu_util_cfs(cpu);
		ns->nr_running += rq->cfs.h_nr_running;
		ns->compute_capacity += capacity_of(cpu);

		if (find_idle && idle_core < 0 && !rq->nr_running && idle_cpu(cpu)) {
			if (READ_ONCE(rq->numa_migrate_on) ||
			    !cpumask_test_cpu(cpu, env->p->cpus_ptr))
				continue;

			if (ns->idle_cpu == -1)
				ns->idle_cpu = cpu;

			idle_core = numa_idle_core(idle_core, cpu);
		}
	}
	rcu_read_unlock();

	ns->weight = cpumask_weight(cpumask_of_node(nid));

	ns->node_type = numa_classify(env->imbalance_pct, ns);

	if (idle_core >= 0)
		ns->idle_cpu = idle_core;
}

static void task_numa_assign(struct task_numa_env *env,
			     struct task_struct *p, long imp)
{
	struct rq *rq = cpu_rq(env->dst_cpu);

	/* Check if run-queue part of active NUMA balance. */
	if (env->best_cpu != env->dst_cpu && xchg(&rq->numa_migrate_on, 1)) {
		int cpu;
		int start = env->dst_cpu;

		/* Find alternative idle CPU. */
		for_each_cpu_wrap(cpu, cpumask_of_node(env->dst_nid), start + 1) {
			if (cpu == env->best_cpu || !idle_cpu(cpu) ||
			    !cpumask_test_cpu(cpu, env->p->cpus_ptr)) {
				continue;
			}

			env->dst_cpu = cpu;
			rq = cpu_rq(env->dst_cpu);
			if (!xchg(&rq->numa_migrate_on, 1))
				goto assign;
		}

		/* Failed to find an alternative idle CPU */
		return;
	}

assign:
	/*
	 * Clear previous best_cpu/rq numa-migrate flag, since task now
	 * found a better CPU to move/swap.
	 */
	if (env->best_cpu != -1 && env->best_cpu != env->dst_cpu) {
		rq = cpu_rq(env->best_cpu);
		WRITE_ONCE(rq->numa_migrate_on, 0);
	}

	if (env->best_task)
		put_task_struct(env->best_task);
	if (p)
		get_task_struct(p);

	env->best_task = p;
	env->best_imp = imp;
	env->best_cpu = env->dst_cpu;
}

static bool load_too_imbalanced(long src_load, long dst_load,
				struct task_numa_env *env)
{
	long imb, old_imb;
	long orig_src_load, orig_dst_load;
	long src_capacity, dst_capacity;

	/*
	 * The load is corrected for the CPU capacity available on each node.
	 *
	 * src_load        dst_load
	 * ------------ vs ---------
	 * src_capacity    dst_capacity
	 */
	src_capacity = env->src_stats.compute_capacity;
	dst_capacity = env->dst_stats.compute_capacity;

	imb = abs(dst_load * src_capacity - src_load * dst_capacity);

	orig_src_load = env->src_stats.load;
	orig_dst_load = env->dst_stats.load;

	old_imb = abs(orig_dst_load * src_capacity - orig_src_load * dst_capacity);

	/* Would this change make things worse? */
	return (imb > old_imb);
}

/*
 * Maximum NUMA importance can be 1998 (2*999);
 * SMALLIMP @ 30 would be close to 1998/64.
 * Used to deter task migration.
 */
#define SMALLIMP	30

/*
 * This checks if the overall compute and NUMA accesses of the system would
 * be improved if the source tasks was migrated to the target dst_cpu taking
 * into account that it might be best if task running on the dst_cpu should
 * be exchanged with the source task
 */
static bool task_numa_compare(struct task_numa_env *env,
			      long taskimp, long groupimp, bool maymove)
{
	struct numa_group *cur_ng, *p_ng = deref_curr_numa_group(env->p);
	struct rq *dst_rq = cpu_rq(env->dst_cpu);
	long imp = p_ng ? groupimp : taskimp;
	struct task_struct *cur;
	long src_load, dst_load;
	int dist = env->dist;
	long moveimp = imp;
	long load;
	bool stopsearch = false;

	if (READ_ONCE(dst_rq->numa_migrate_on))
		return false;

	rcu_read_lock();
	cur = rcu_dereference(dst_rq->curr);
	if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur)))
		cur = NULL;

	/*
	 * Because we have preemption enabled we can get migrated around and
	 * end try selecting ourselves (current == env->p) as a swap candidate.
	 */
	if (cur == env->p) {
		stopsearch = true;
		goto unlock;
	}

	if (!cur) {
		if (maymove && moveimp >= env->best_imp)
			goto assign;
		else
			goto unlock;
	}

	/* Skip this swap candidate if cannot move to the source cpu. */
	if (!cpumask_test_cpu(env->src_cpu, cur->cpus_ptr))
		goto unlock;

	/*
	 * Skip this swap candidate if it is not moving to its preferred
	 * node and the best task is.
	 */
	if (env->best_task &&
	    env->best_task->numa_preferred_nid == env->src_nid &&
	    cur->numa_preferred_nid != env->src_nid) {
		goto unlock;
	}

	/*
	 * "imp" is the fault differential for the source task between the
	 * source and destination node. Calculate the total differential for
	 * the source task and potential destination task. The more negative
	 * the value is, the more remote accesses that would be expected to
	 * be incurred if the tasks were swapped.
	 *
	 * If dst and source tasks are in the same NUMA group, or not
	 * in any group then look only at task weights.
	 */
	cur_ng = rcu_dereference(cur->numa_group);
	if (cur_ng == p_ng) {
		/*
		 * Do not swap within a group or between tasks that have
		 * no group if there is spare capacity. Swapping does
		 * not address the load imbalance and helps one task at
		 * the cost of punishing another.
		 */
		if (env->dst_stats.node_type == node_has_spare)
			goto unlock;

		imp = taskimp + task_weight(cur, env->src_nid, dist) -
		      task_weight(cur, env->dst_nid, dist);
		/*
		 * Add some hysteresis to prevent swapping the
		 * tasks within a group over tiny differences.
		 */
		if (cur_ng)
			imp -= imp / 16;
	} else {
		/*
		 * Compare the group weights. If a task is all by itself
		 * (not part of a group), use the task weight instead.
		 */
		if (cur_ng && p_ng)
			imp += group_weight(cur, env->src_nid, dist) -
			       group_weight(cur, env->dst_nid, dist);
		else
			imp += task_weight(cur, env->src_nid, dist) -
			       task_weight(cur, env->dst_nid, dist);
	}

	/* Discourage picking a task already on its preferred node */
	if (cur->numa_preferred_nid == env->dst_nid)
		imp -= imp / 16;

	/*
	 * Encourage picking a task that moves to its preferred node.
	 * This potentially makes imp larger than it's maximum of
	 * 1998 (see SMALLIMP and task_weight for why) but in this
	 * case, it does not matter.
	 */
	if (cur->numa_preferred_nid == env->src_nid)
		imp += imp / 8;

	if (maymove && moveimp > imp && moveimp > env->best_imp) {
		imp = moveimp;
		cur = NULL;
		goto assign;
	}

	/*
	 * Prefer swapping with a task moving to its preferred node over a
	 * task that is not.
	 */
	if (env->best_task && cur->numa_preferred_nid == env->src_nid &&
	    env->best_task->numa_preferred_nid != env->src_nid) {
		goto assign;
	}

	/*
	 * If the NUMA importance is less than SMALLIMP,
	 * task migration might only result in ping pong
	 * of tasks and also hurt performance due to cache
	 * misses.
	 */
	if (imp < SMALLIMP || imp <= env->best_imp + SMALLIMP / 2)
		goto unlock;

	/*
	 * In the overloaded case, try and keep the load balanced.
	 */
	load = task_h_load(env->p) - task_h_load(cur);
	if (!load)
		goto assign;

	dst_load = env->dst_stats.load + load;
	src_load = env->src_stats.load - load;

	if (load_too_imbalanced(src_load, dst_load, env))
		goto unlock;

assign:
	/* Evaluate an idle CPU for a task numa move. */
	if (!cur) {
		int cpu = env->dst_stats.idle_cpu;

		/* Nothing cached so current CPU went idle since the search. */
		if (cpu < 0)
			cpu = env->dst_cpu;

		/*
		 * If the CPU is no longer truly idle and the previous best CPU
		 * is, keep using it.
		 */
		if (!idle_cpu(cpu) && env->best_cpu >= 0 &&
		    idle_cpu(env->best_cpu)) {
			cpu = env->best_cpu;
		}

		env->dst_cpu = cpu;
	}

	task_numa_assign(env, cur, imp);

	/*
	 * If a move to idle is allowed because there is capacity or load
	 * balance improves then stop the search. While a better swap
	 * candidate may exist, a search is not free.
	 */
	if (maymove && !cur && env->best_cpu >= 0 && idle_cpu(env->best_cpu))
		stopsearch = true;

	/*
	 * If a swap candidate must be identified and the current best task
	 * moves its preferred node then stop the search.
	 */
	if (!maymove && env->best_task &&
	    env->best_task->numa_preferred_nid == env->src_nid) {
		stopsearch = true;
	}
unlock:
	rcu_read_unlock();

	return stopsearch;
}

static void task_numa_find_cpu(struct task_numa_env *env,
				long taskimp, long groupimp)
{
	bool maymove = false;
	int cpu;

	/*
	 * If dst node has spare capacity, then check if there is an
	 * imbalance that would be overruled by the load balancer.
	 */
	if (env->dst_stats.node_type == node_has_spare) {
		unsigned int imbalance;
		int src_running, dst_running;

		/*
		 * Would movement cause an imbalance? Note that if src has
		 * more running tasks that the imbalance is ignored as the
		 * move improves the imbalance from the perspective of the
		 * CPU load balancer.
		 * */
		src_running = env->src_stats.nr_running - 1;
		dst_running = env->dst_stats.nr_running + 1;
		imbalance = max(0, dst_running - src_running);
		imbalance = adjust_numa_imbalance(imbalance, dst_running,
						  env->imb_numa_nr);

		/* Use idle CPU if there is no imbalance */
		if (!imbalance) {
			maymove = true;
			if (env->dst_stats.idle_cpu >= 0) {
				env->dst_cpu = env->dst_stats.idle_cpu;
				task_numa_assign(env, NULL, 0);
				return;
			}
		}
	} else {
		long src_load, dst_load, load;
		/*
		 * If the improvement from just moving env->p direction is better
		 * than swapping tasks around, check if a move is possible.
		 */
		load = task_h_load(env->p);
		dst_load = env->dst_stats.load + load;
		src_load = env->src_stats.load - load;
		maymove = !load_too_imbalanced(src_load, dst_load, env);
	}

	for_each_cpu(cpu, cpumask_of_node(env->dst_nid)) {
		/* Skip this CPU if the source task cannot migrate */
		if (!cpumask_test_cpu(cpu, env->p->cpus_ptr))
			continue;

		env->dst_cpu = cpu;
		if (task_numa_compare(env, taskimp, groupimp, maymove))
			break;
	}
}

static int task_numa_migrate(struct task_struct *p)
{
	struct task_numa_env env = {
		.p = p,

		.src_cpu = task_cpu(p),
		.src_nid = task_node(p),

		.imbalance_pct = 112,

		.best_task = NULL,
		.best_imp = 0,
		.best_cpu = -1,
	};
	unsigned long taskweight, groupweight;
	struct sched_domain *sd;
	long taskimp, groupimp;
	struct numa_group *ng;
	struct rq *best_rq;
	int nid, ret, dist;

	/*
	 * Pick the lowest SD_NUMA domain, as that would have the smallest
	 * imbalance and would be the first to start moving tasks about.
	 *
	 * And we want to avoid any moving of tasks about, as that would create
	 * random movement of tasks -- counter the numa conditions we're trying
	 * to satisfy here.
	 */
	rcu_read_lock();
	sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu));
	if (sd) {
		env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
		env.imb_numa_nr = sd->imb_numa_nr;
	}
	rcu_read_unlock();

	/*
	 * Cpusets can break the scheduler domain tree into smaller
	 * balance domains, some of which do not cross NUMA boundaries.
	 * Tasks that are "trapped" in such domains cannot be migrated
	 * elsewhere, so there is no point in (re)trying.
	 */
	if (unlikely(!sd)) {
		sched_setnuma(p, task_node(p));
		return -EINVAL;
	}

	env.dst_nid = p->numa_preferred_nid;
	dist = env.dist = node_distance(env.src_nid, env.dst_nid);
	taskweight = task_weight(p, env.src_nid, dist);
	groupweight = group_weight(p, env.src_nid, dist);
	update_numa_stats(&env, &env.src_stats, env.src_nid, false);
	taskimp = task_weight(p, env.dst_nid, dist) - taskweight;
	groupimp = group_weight(p, env.dst_nid, dist) - groupweight;
	update_numa_stats(&env, &env.dst_stats, env.dst_nid, true);

	/* Try to find a spot on the preferred nid. */
	task_numa_find_cpu(&env, taskimp, groupimp);

	/*
	 * Look at other nodes in these cases:
	 * - there is no space available on the preferred_nid
	 * - the task is part of a numa_group that is interleaved across
	 *   multiple NUMA nodes; in order to better consolidate the group,
	 *   we need to check other locations.
	 */
	ng = deref_curr_numa_group(p);
	if (env.best_cpu == -1 || (ng && ng->active_nodes > 1)) {
		for_each_node_state(nid, N_CPU) {
			if (nid == env.src_nid || nid == p->numa_preferred_nid)
				continue;

			dist = node_distance(env.src_nid, env.dst_nid);
			if (sched_numa_topology_type == NUMA_BACKPLANE &&
						dist != env.dist) {
				taskweight = task_weight(p, env.src_nid, dist);
				groupweight = group_weight(p, env.src_nid, dist);
			}

			/* Only consider nodes where both task and groups benefit */
			taskimp = task_weight(p, nid, dist) - taskweight;
			groupimp = group_weight(p, nid, dist) - groupweight;
			if (taskimp < 0 && groupimp < 0)
				continue;

			env.dist = dist;
			env.dst_nid = nid;
			update_numa_stats(&env, &env.dst_stats, env.dst_nid, true);
			task_numa_find_cpu(&env, taskimp, groupimp);
		}
	}

	/*
	 * If the task is part of a workload that spans multiple NUMA nodes,
	 * and is migrating into one of the workload's active nodes, remember
	 * this node as the task's preferred numa node, so the workload can
	 * settle down.
	 * A task that migrated to a second choice node will be better off
	 * trying for a better one later. Do not set the preferred node here.
	 */
	if (ng) {
		if (env.best_cpu == -1)
			nid = env.src_nid;
		else
			nid = cpu_to_node(env.best_cpu);

		if (nid != p->numa_preferred_nid)
			sched_setnuma(p, nid);
	}

	/* No better CPU than the current one was found. */
	if (env.best_cpu == -1) {
		trace_sched_stick_numa(p, env.src_cpu, NULL, -1);
		return -EAGAIN;
	}

	best_rq = cpu_rq(env.best_cpu);
	if (env.best_task == NULL) {
		ret = migrate_task_to(p, env.best_cpu);
		WRITE_ONCE(best_rq->numa_migrate_on, 0);
		if (ret != 0)
			trace_sched_stick_numa(p, env.src_cpu, NULL, env.best_cpu);
		return ret;
	}

	ret = migrate_swap(p, env.best_task, env.best_cpu, env.src_cpu);
	WRITE_ONCE(best_rq->numa_migrate_on, 0);

	if (ret != 0)
		trace_sched_stick_numa(p, env.src_cpu, env.best_task, env.best_cpu);
	put_task_struct(env.best_task);
	return ret;
}

/* Attempt to migrate a task to a CPU on the preferred node. */
static void numa_migrate_preferred(struct task_struct *p)
{
	unsigned long interval = HZ;

	/* This task has no NUMA fault statistics yet */
	if (unlikely(p->numa_preferred_nid == NUMA_NO_NODE || !p->numa_faults))
		return;

	/* Periodically retry migrating the task to the preferred node */
	interval = min(interval, msecs_to_jiffies(p->numa_scan_period) / 16);
	p->numa_migrate_retry = jiffies + interval;

	/* Success if task is already running on preferred CPU */
	if (task_node(p) == p->numa_preferred_nid)
		return;

	/* Otherwise, try migrate to a CPU on the preferred node */
	task_numa_migrate(p);
}

/*
 * Find out how many nodes the workload is actively running on. Do this by
 * tracking the nodes from which NUMA hinting faults are triggered. This can
 * be different from the set of nodes where the workload's memory is currently
 * located.
 */
static void numa_group_count_active_nodes(struct numa_group *numa_group)
{
	unsigned long faults, max_faults = 0;
	int nid, active_nodes = 0;

	for_each_node_state(nid, N_CPU) {
		faults = group_faults_cpu(numa_group, nid);
		if (faults > max_faults)
			max_faults = faults;
	}

	for_each_node_state(nid, N_CPU) {
		faults = group_faults_cpu(numa_group, nid);
		if (faults * ACTIVE_NODE_FRACTION > max_faults)
			active_nodes++;
	}

	numa_group->max_faults_cpu = max_faults;
	numa_group->active_nodes = active_nodes;
}

/*
 * When adapting the scan rate, the period is divided into NUMA_PERIOD_SLOTS
 * increments. The more local the fault statistics are, the higher the scan
 * period will be for the next scan window. If local/(local+remote) ratio is
 * below NUMA_PERIOD_THRESHOLD (where range of ratio is 1..NUMA_PERIOD_SLOTS)
 * the scan period will decrease. Aim for 70% local accesses.
 */
#define NUMA_PERIOD_SLOTS 10
#define NUMA_PERIOD_THRESHOLD 7

/*
 * Increase the scan period (slow down scanning) if the majority of
 * our memory is already on our local node, or if the majority of
 * the page accesses are shared with other processes.
 * Otherwise, decrease the scan period.
 */
static void update_task_scan_period(struct task_struct *p,
			unsigned long shared, unsigned long private)
{
	unsigned int period_slot;
	int lr_ratio, ps_ratio;
	int diff;

	unsigned long remote = p->numa_faults_locality[0];
	unsigned long local = p->numa_faults_locality[1];

	/*
	 * If there were no record hinting faults then either the task is
	 * completely idle or all activity is in areas that are not of interest
	 * to automatic numa balancing. Related to that, if there were failed
	 * migration then it implies we are migrating too quickly or the local
	 * node is overloaded. In either case, scan slower
	 */
	if (local + shared == 0 || p->numa_faults_locality[2]) {
		p->numa_scan_period = min(p->numa_scan_period_max,
			p->numa_scan_period << 1);

		p->mm->numa_next_scan = jiffies +
			msecs_to_jiffies(p->numa_scan_period);

		return;
	}

	/*
	 * Prepare to scale scan period relative to the current period.
	 *	 == NUMA_PERIOD_THRESHOLD scan period stays the same
	 *       <  NUMA_PERIOD_THRESHOLD scan period decreases (scan faster)
	 *	 >= NUMA_PERIOD_THRESHOLD scan period increases (scan slower)
	 */
	period_slot = DIV_ROUND_UP(p->numa_scan_period, NUMA_PERIOD_SLOTS);
	lr_ratio = (local * NUMA_PERIOD_SLOTS) / (local + remote);
	ps_ratio = (private * NUMA_PERIOD_SLOTS) / (private + shared);

	if (ps_ratio >= NUMA_PERIOD_THRESHOLD) {
		/*
		 * Most memory accesses are local. There is no need to
		 * do fast NUMA scanning, since memory is already local.
		 */
		int slot = ps_ratio - NUMA_PERIOD_THRESHOLD;
		if (!slot)
			slot = 1;
		diff = slot * period_slot;
	} else if (lr_ratio >= NUMA_PERIOD_THRESHOLD) {
		/*
		 * Most memory accesses are shared with other tasks.
		 * There is no point in continuing fast NUMA scanning,
		 * since other tasks may just move the memory elsewhere.
		 */
		int slot = lr_ratio - NUMA_PERIOD_THRESHOLD;
		if (!slot)
			slot = 1;
		diff = slot * period_slot;
	} else {
		/*
		 * Private memory faults exceed (SLOTS-THRESHOLD)/SLOTS,
		 * yet they are not on the local NUMA node. Speed up
		 * NUMA scanning to get the memory moved over.
		 */
		int ratio = max(lr_ratio, ps_ratio);
		diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot;
	}

	p->numa_scan_period = clamp(p->numa_scan_period + diff,
			task_scan_min(p), task_scan_max(p));
	memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
}

/*
 * Get the fraction of time the task has been running since the last
 * NUMA placement cycle. The scheduler keeps similar statistics, but
 * decays those on a 32ms period, which is orders of magnitude off
 * from the dozens-of-seconds NUMA balancing period. Use the scheduler
 * stats only if the task is so new there are no NUMA statistics yet.
 */
static u64 numa_get_avg_runtime(struct task_struct *p, u64 *period)
{
	u64 runtime, delta, now;
	/* Use the start of this time slice to avoid calculations. */
	now = p->se.exec_start;
	runtime = p->se.sum_exec_runtime;

	if (p->last_task_numa_placement) {
		delta = runtime - p->last_sum_exec_runtime;
		*period = now - p->last_task_numa_placement;

		/* Avoid time going backwards, prevent potential divide error: */
		if (unlikely((s64)*period < 0))
			*period = 0;
	} else {
		delta = p->se.avg.load_sum;
		*period = LOAD_AVG_MAX;
	}

	p->last_sum_exec_runtime = runtime;
	p->last_task_numa_placement = now;

	return delta;
}

/*
 * Determine the preferred nid for a task in a numa_group. This needs to
 * be done in a way that produces consistent results with group_weight,
 * otherwise workloads might not converge.
 */
static int preferred_group_nid(struct task_struct *p, int nid)
{
	nodemask_t nodes;
	int dist;

	/* Direct connections between all NUMA nodes. */
	if (sched_numa_topology_type == NUMA_DIRECT)
		return nid;

	/*
	 * On a system with glueless mesh NUMA topology, group_weight
	 * scores nodes according to the number of NUMA hinting faults on
	 * both the node itself, and on nearby nodes.
	 */
	if (sched_numa_topology_type == NUMA_GLUELESS_MESH) {
		unsigned long score, max_score = 0;
		int node, max_node = nid;

		dist = sched_max_numa_distance;

		for_each_node_state(node, N_CPU) {
			score = group_weight(p, node, dist);
			if (score > max_score) {
				max_score = score;
				max_node = node;
			}
		}
		return max_node;
	}

	/*
	 * Finding the preferred nid in a system with NUMA backplane
	 * interconnect topology is more involved. The goal is to locate
	 * tasks from numa_groups near each other in the system, and
	 * untangle workloads from different sides of the system. This requires
	 * searching down the hierarchy of node groups, recursively searching
	 * inside the highest scoring group of nodes. The nodemask tricks
	 * keep the complexity of the search down.
	 */
	nodes = node_states[N_CPU];
	for (dist = sched_max_numa_distance; dist > LOCAL_DISTANCE; dist--) {
		unsigned long max_faults = 0;
		nodemask_t max_group = NODE_MASK_NONE;
		int a, b;

		/* Are there nodes at this distance from each other? */
		if (!find_numa_distance(dist))
			continue;

		for_each_node_mask(a, nodes) {
			unsigned long faults = 0;
			nodemask_t this_group;
			nodes_clear(this_group);

			/* Sum group's NUMA faults; includes a==b case. */
			for_each_node_mask(b, nodes) {
				if (node_distance(a, b) < dist) {
					faults += group_faults(p, b);
					node_set(b, this_group);
					node_clear(b, nodes);
				}
			}

			/* Remember the top group. */
			if (faults > max_faults) {
				max_faults = faults;
				max_group = this_group;
				/*
				 * subtle: at the smallest distance there is
				 * just one node left in each "group", the
				 * winner is the preferred nid.
				 */
				nid = a;
			}
		}
		/* Next round, evaluate the nodes within max_group. */
		if (!max_faults)
			break;
		nodes = max_group;
	}
	return nid;
}

static void task_numa_placement(struct task_struct *p)
{
	int seq, nid, max_nid = NUMA_NO_NODE;
	unsigned long max_faults = 0;
	unsigned long fault_types[2] = { 0, 0 };
	unsigned long total_faults;
	u64 runtime, period;
	spinlock_t *group_lock = NULL;
	struct numa_group *ng;

	/*
	 * The p->mm->numa_scan_seq field gets updated without
	 * exclusive access. Use READ_ONCE() here to ensure
	 * that the field is read in a single access:
	 */
	seq = READ_ONCE(p->mm->numa_scan_seq);
	if (p->numa_scan_seq == seq)
		return;
	p->numa_scan_seq = seq;
	p->numa_scan_period_max = task_scan_max(p);

	total_faults = p->numa_faults_locality[0] +
		       p->numa_faults_locality[1];
	runtime = numa_get_avg_runtime(p, &period);

	/* If the task is part of a group prevent parallel updates to group stats */
	ng = deref_curr_numa_group(p);
	if (ng) {
		group_lock = &ng->lock;
		spin_lock_irq(group_lock);
	}

	/* Find the node with the highest number of faults */
	for_each_online_node(nid) {
		/* Keep track of the offsets in numa_faults array */
		int mem_idx, membuf_idx, cpu_idx, cpubuf_idx;
		unsigned long faults = 0, group_faults = 0;
		int priv;

		for (priv = 0; priv < NR_NUMA_HINT_FAULT_TYPES; priv++) {
			long diff, f_diff, f_weight;

			mem_idx = task_faults_idx(NUMA_MEM, nid, priv);
			membuf_idx = task_faults_idx(NUMA_MEMBUF, nid, priv);
			cpu_idx = task_faults_idx(NUMA_CPU, nid, priv);
			cpubuf_idx = task_faults_idx(NUMA_CPUBUF, nid, priv);

			/* Decay existing window, copy faults since last scan */
			diff = p->numa_faults[membuf_idx] - p->numa_faults[mem_idx] / 2;
			fault_types[priv] += p->numa_faults[membuf_idx];
			p->numa_faults[membuf_idx] = 0;

			/*
			 * Normalize the faults_from, so all tasks in a group
			 * count according to CPU use, instead of by the raw
			 * number of faults. Tasks with little runtime have
			 * little over-all impact on throughput, and thus their
			 * faults are less important.
			 */
			f_weight = div64_u64(runtime << 16, period + 1);
			f_weight = (f_weight * p->numa_faults[cpubuf_idx]) /
				   (total_faults + 1);
			f_diff = f_weight - p->numa_faults[cpu_idx] / 2;
			p->numa_faults[cpubuf_idx] = 0;

			p->numa_faults[mem_idx] += diff;
			p->numa_faults[cpu_idx] += f_diff;
			faults += p->numa_faults[mem_idx];
			p->total_numa_faults += diff;
			if (ng) {
				/*
				 * safe because we can only change our own group
				 *
				 * mem_idx represents the offset for a given
				 * nid and priv in a specific region because it
				 * is at the beginning of the numa_faults array.
				 */
				ng->faults[mem_idx] += diff;
				ng->faults[cpu_idx] += f_diff;
				ng->total_faults += diff;
				group_faults += ng->faults[mem_idx];
			}
		}

		if (!ng) {
			if (faults > max_faults) {
				max_faults = faults;
				max_nid = nid;
			}
		} else if (group_faults > max_faults) {
			max_faults = group_faults;
			max_nid = nid;
		}
	}

	/* Cannot migrate task to CPU-less node */
	max_nid = numa_nearest_node(max_nid, N_CPU);

	if (ng) {
		numa_group_count_active_nodes(ng);
		spin_unlock_irq(group_lock);
		max_nid = preferred_group_nid(p, max_nid);
	}

	if (max_faults) {
		/* Set the new preferred node */
		if (max_nid != p->numa_preferred_nid)
			sched_setnuma(p, max_nid);
	}

	update_task_scan_period(p, fault_types[0], fault_types[1]);
}

static inline int get_numa_group(struct numa_group *grp)
{
	return refcount_inc_not_zero(&grp->refcount);
}

static inline void put_numa_group(struct numa_group *grp)
{
	if (refcount_dec_and_test(&grp->refcount))
		kfree_rcu(grp, rcu);
}

static void task_numa_group(struct task_struct *p, int cpupid, int flags,
			int *priv)
{
	struct numa_group *grp, *my_grp;
	struct task_struct *tsk;
	bool join = false;
	int cpu = cpupid_to_cpu(cpupid);
	int i;

	if (unlikely(!deref_curr_numa_group(p))) {
		unsigned int size = sizeof(struct numa_group) +
				    NR_NUMA_HINT_FAULT_STATS *
				    nr_node_ids * sizeof(unsigned long);

		grp = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
		if (!grp)
			return;

		refcount_set(&grp->refcount, 1);
		grp->active_nodes = 1;
		grp->max_faults_cpu = 0;
		spin_lock_init(&grp->lock);
		grp->gid = p->pid;

		for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
			grp->faults[i] = p->numa_faults[i];

		grp->total_faults = p->total_numa_faults;

		grp->nr_tasks++;
		rcu_assign_pointer(p->numa_group, grp);
	}

	rcu_read_lock();
	tsk = READ_ONCE(cpu_rq(cpu)->curr);

	if (!cpupid_match_pid(tsk, cpupid))
		goto no_join;

	grp = rcu_dereference(tsk->numa_group);
	if (!grp)
		goto no_join;

	my_grp = deref_curr_numa_group(p);
	if (grp == my_grp)
		goto no_join;

	/*
	 * Only join the other group if its bigger; if we're the bigger group,
	 * the other task will join us.
	 */
	if (my_grp->nr_tasks > grp->nr_tasks)
		goto no_join;

	/*
	 * Tie-break on the grp address.
	 */
	if (my_grp->nr_tasks == grp->nr_tasks && my_grp > grp)
		goto no_join;

	/* Always join threads in the same process. */
	if (tsk->mm == current->mm)
		join = true;

	/* Simple filter to avoid false positives due to PID collisions */
	if (flags & TNF_SHARED)
		join = true;

	/* Update priv based on whether false sharing was detected */
	*priv = !join;

	if (join && !get_numa_group(grp))
		goto no_join;

	rcu_read_unlock();

	if (!join)
		return;

	WARN_ON_ONCE(irqs_disabled());
	double_lock_irq(&my_grp->lock, &grp->lock);

	for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
		my_grp->faults[i] -= p->numa_faults[i];
		grp->faults[i] += p->numa_faults[i];
	}
	my_grp->total_faults -= p->total_numa_faults;
	grp->total_faults += p->total_numa_faults;

	my_grp->nr_tasks--;
	grp->nr_tasks++;

	spin_unlock(&my_grp->lock);
	spin_unlock_irq(&grp->lock);

	rcu_assign_pointer(p->numa_group, grp);

	put_numa_group(my_grp);
	return;

no_join:
	rcu_read_unlock();
	return;
}

/*
 * Get rid of NUMA statistics associated with a task (either current or dead).
 * If @final is set, the task is dead and has reached refcount zero, so we can
 * safely free all relevant data structures. Otherwise, there might be
 * concurrent reads from places like load balancing and procfs, and we should
 * reset the data back to default state without freeing ->numa_faults.
 */
void task_numa_free(struct task_struct *p, bool final)
{
	/* safe: p either is current or is being freed by current */
	struct numa_group *grp = rcu_dereference_raw(p->numa_group);
	unsigned long *numa_faults = p->numa_faults;
	unsigned long flags;
	int i;

	if (!numa_faults)
		return;

	if (grp) {
		spin_lock_irqsave(&grp->lock, flags);
		for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
			grp->faults[i] -= p->numa_faults[i];
		grp->total_faults -= p->total_numa_faults;

		grp->nr_tasks--;
		spin_unlock_irqrestore(&grp->lock, flags);
		RCU_INIT_POINTER(p->numa_group, NULL);
		put_numa_group(grp);
	}

	if (final) {
		p->numa_faults = NULL;
		kfree(numa_faults);
	} else {
		p->total_numa_faults = 0;
		for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
			numa_faults[i] = 0;
	}
}

/*
 * Got a PROT_NONE fault for a page on @node.
 */
void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
{
	struct task_struct *p = current;
	bool migrated = flags & TNF_MIGRATED;
	int cpu_node = task_node(current);
	int local = !!(flags & TNF_FAULT_LOCAL);
	struct numa_group *ng;
	int priv;

	if (!static_branch_likely(&sched_numa_balancing))
		return;

	/* for example, ksmd faulting in a user's mm */
	if (!p->mm)
		return;

	/*
	 * NUMA faults statistics are unnecessary for the slow memory
	 * node for memory tiering mode.
	 */
	if (!node_is_toptier(mem_node) &&
	    (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING ||
	     !cpupid_valid(last_cpupid)))
		return;

	/* Allocate buffer to track faults on a per-node basis */
	if (unlikely(!p->numa_faults)) {
		int size = sizeof(*p->numa_faults) *
			   NR_NUMA_HINT_FAULT_BUCKETS * nr_node_ids;

		p->numa_faults = kzalloc(size, GFP_KERNEL|__GFP_NOWARN);
		if (!p->numa_faults)
			return;

		p->total_numa_faults = 0;
		memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
	}

	/*
	 * First accesses are treated as private, otherwise consider accesses
	 * to be private if the accessing pid has not changed
	 */
	if (unlikely(last_cpupid == (-1 & LAST_CPUPID_MASK))) {
		priv = 1;
	} else {
		priv = cpupid_match_pid(p, last_cpupid);
		if (!priv && !(flags & TNF_NO_GROUP))
			task_numa_group(p, last_cpupid, flags, &priv);
	}

	/*
	 * If a workload spans multiple NUMA nodes, a shared fault that
	 * occurs wholly within the set of nodes that the workload is
	 * actively using should be counted as local. This allows the
	 * scan rate to slow down when a workload has settled down.
	 */
	ng = deref_curr_numa_group(p);
	if (!priv && !local && ng && ng->active_nodes > 1 &&
				numa_is_active_node(cpu_node, ng) &&
				numa_is_active_node(mem_node, ng))
		local = 1;

	/*
	 * Retry to migrate task to preferred node periodically, in case it
	 * previously failed, or the scheduler moved us.
	 */
	if (time_after(jiffies, p->numa_migrate_retry)) {
		task_numa_placement(p);
		numa_migrate_preferred(p);
	}

	if (migrated)
		p->numa_pages_migrated += pages;
	if (flags & TNF_MIGRATE_FAIL)
		p->numa_faults_locality[2] += pages;

	p->numa_faults[task_faults_idx(NUMA_MEMBUF, mem_node, priv)] += pages;
	p->numa_faults[task_faults_idx(NUMA_CPUBUF, cpu_node, priv)] += pages;
	p->numa_faults_locality[local] += pages;
}

static void reset_ptenuma_scan(struct task_struct *p)
{
	/*
	 * We only did a read acquisition of the mmap sem, so
	 * p->mm->numa_scan_seq is written to without exclusive access
	 * and the update is not guaranteed to be atomic. That's not
	 * much of an issue though, since this is just used for
	 * statistical sampling. Use READ_ONCE/WRITE_ONCE, which are not
	 * expensive, to avoid any form of compiler optimizations:
	 */
	WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
	p->mm->numa_scan_offset = 0;
}

static bool vma_is_accessed(struct mm_struct *mm, struct vm_area_struct *vma)
{
	unsigned long pids;
	/*
	 * 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) - vma->numab_state->start_scan_seq) < 2)
		return true;

	pids = vma->numab_state->pids_active[0] | vma->numab_state->pids_active[1];
	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;
	}

	return false;
}

#define VMA_PID_RESET_PERIOD (4 * sysctl_numa_balancing_scan_delay)

/*
 * The expensive part of numa migration is done from task_work context.
 * Triggered from task_tick_numa().
 */
static 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;
	u64 runtime = p->se.sum_exec_runtime;
	struct vm_area_struct *vma;
	unsigned long start, end;
	unsigned long nr_pte_updates = 0;
	long pages, virtpages;
	struct vma_iterator vmi;
	bool vma_pids_skipped;
	bool vma_pids_forced = false;

	SCHED_WARN_ON(p != container_of(work, struct task_struct, numa_work));

	work->next = work;
	/*
	 * Who cares about NUMA placement when they're dying.
	 *
	 * NOTE: make sure not to dereference p->mm before this check,
	 * exit_task_work() happens _after_ exit_mm() so we could be called
	 * without p->mm even though we still had it when we enqueued this
	 * work.
	 */
	if (p->flags & PF_EXITING)
		return;

	if (!mm->numa_next_scan) {
		mm->numa_next_scan = now +
			msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
	}

	/*
	 * Enforce maximal scan/migration frequency..
	 */
	migrate = mm->numa_next_scan;
	if (time_before(now, migrate))
		return;

	if (p->numa_scan_period == 0) {
		p->numa_scan_period_max = task_scan_max(p);
		p->numa_scan_period = task_scan_start(p);
	}

	next_scan = now + msecs_to_jiffies(p->numa_scan_period);
	if (!try_cmpxchg(&mm->numa_next_scan, &migrate, next_scan))
		return;

	/*
	 * Delay this task enough that another task of this mm will likely win
	 * the next time around.
	 */
	p->node_stamp += 2 * TICK_NSEC;

	pages = sysctl_numa_balancing_scan_size;
	pages <<= 20 - PAGE_SHIFT; /* MB in pages */