Commit 5bca2303 authored by Mel Gorman's avatar Mel Gorman
Browse files

mm: sched: numa: Delay PTE scanning until a task is scheduled on a new node 



Due to the fact that migrations are driven by the CPU a task is running
on there is no point tracking NUMA faults until one task runs on a new
node. This patch tracks the first node used by an address space. Until
it changes, PTE scanning is disabled and no NUMA hinting faults are
trapped. This should help workloads that are short-lived, do not care
about NUMA placement or have bound themselves to a single node.

This takes advantage of the logic in "mm: sched: numa: Implement slow
start for working set sampling" to delay when the checks are made. This
will take advantage of processes that set their CPU and node bindings
early in their lifetime. It will also potentially allow any initial load
balancing to take place.

Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
parent 3105b86a

include/linux/mm_types.h

+10 −0
Original line number Original line Diff line number Diff line
@@ -418,10 +418,20 @@ struct mm_struct { 




	/* numa_scan_seq prevents two threads setting pte_numa */

	/* numa_scan_seq prevents two threads setting pte_numa */

	int numa_scan_seq;

	int numa_scan_seq;



	/*

	 * The first node a task was scheduled on. If a task runs on

	 * a different node than Make PTE Scan Go Now.

	 */

	int first_nid;

#endif

#endif

	struct uprobes_state uprobes_state;

	struct uprobes_state uprobes_state;

};

};





/* first nid will either be a valid NID or one of these values */

#define NUMA_PTE_SCAN_INIT	-1

#define NUMA_PTE_SCAN_ACTIVE	-2



static inline void mm_init_cpumask(struct mm_struct *mm)

static inline void mm_init_cpumask(struct mm_struct *mm)

{

{

#ifdef CONFIG_CPUMASK_OFFSTACK

#ifdef CONFIG_CPUMASK_OFFSTACK

kernel/fork.c

+3 −0
Original line number Original line Diff line number Diff line
@@ -820,6 +820,9 @@ struct mm_struct *dup_mm(struct task_struct *tsk) 




#ifdef CONFIG_TRANSPARENT_HUGEPAGE

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

	mm->pmd_huge_pte = NULL;

	mm->pmd_huge_pte = NULL;

#endif

#ifdef CONFIG_NUMA_BALANCING

	mm->first_nid = NUMA_PTE_SCAN_INIT;

#endif

#endif

	if (!mm_init(mm, tsk))

	if (!mm_init(mm, tsk))

		goto fail_nomem;

		goto fail_nomem;

kernel/sched/fair.c

+18 −0
Original line number Original line Diff line number Diff line
@@ -860,6 +860,24 @@ void task_numa_work(struct callback_head *work) 
	if (p->flags & PF_EXITING)

	if (p->flags & PF_EXITING)

		return;

		return;





	/*

	 * We do not care about task placement until a task runs on a node

	 * other than the first one used by the address space. This is

	 * largely because migrations are driven by what CPU the task

	 * is running on. If it's never scheduled on another node, it'll

	 * not migrate so why bother trapping the fault.

	 */

	if (mm->first_nid == NUMA_PTE_SCAN_INIT)

		mm->first_nid = numa_node_id();

	if (mm->first_nid != NUMA_PTE_SCAN_ACTIVE) {

		/* Are we running on a new node yet? */

		if (numa_node_id() == mm->first_nid &&

		    !sched_feat_numa(NUMA_FORCE))

			return;



		mm->first_nid = NUMA_PTE_SCAN_ACTIVE;

	}



	/*

	/*

	 * Reset the scan period if enough time has gone by. Objective is that

	 * Reset the scan period if enough time has gone by. Objective is that

	 * scanning will be reduced if pages are properly placed. As tasks

	 * scanning will be reduced if pages are properly placed. As tasks

kernel/sched/features.h

+3 −1
Original line number Original line Diff line number Diff line
@@ -65,8 +65,10 @@ SCHED_FEAT(LB_MIN, false) 
/*

/*

 * Apply the automatic NUMA scheduling policy. Enabled automatically

 * Apply the automatic NUMA scheduling policy. Enabled automatically

 * at runtime if running on a NUMA machine. Can be controlled via

 * at runtime if running on a NUMA machine. Can be controlled via

 * numa_balancing=

 * numa_balancing=. Allow PTE scanning to be forced on UMA machines

 * for debugging the core machinery.

 */

 */

#ifdef CONFIG_NUMA_BALANCING

#ifdef CONFIG_NUMA_BALANCING

SCHED_FEAT(NUMA,	false)

SCHED_FEAT(NUMA,	false)

SCHED_FEAT(NUMA_FORCE,	false)

#endif
 
#endif

CRA Git | Maintained and supported by SUSTech CRA and CCSE