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Commit dabe1d99 authored by Rik van Riel's avatar Rik van Riel Committed by Ingo Molnar
Browse files

sched/numa: Be more careful about joining numa groups 



Due to the way the pid is truncated, and tasks are moved between
CPUs by the scheduler, it is possible for the current task_numa_fault
to group together tasks that do not actually share memory together.

This patch adds a few easy sanity checks to task_numa_fault, joining
tasks together if they share the same tsk->mm, or if the fault was on
a page with an elevated mapcount, in a shared VMA.

Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-57-git-send-email-mgorman@suse.de


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 0ec8aa00

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -1454,6 +1454,7 @@ struct task_struct { 


#define TNF_MIGRATED	0x01

#define TNF_NO_GROUP	0x02

#define TNF_SHARED	0x04



#ifdef CONFIG_NUMA_BALANCING

extern void task_numa_fault(int last_node, int node, int pages, int flags);

kernel/sched/fair.c

+11 −5
Original line number Diff line number Diff line
@@ -1381,7 +1381,7 @@ static void double_lock(spinlock_t *l1, spinlock_t *l2) 
	spin_lock_nested(l2, SINGLE_DEPTH_NESTING);

}



static void task_numa_group(struct task_struct *p, int cpupid)

static void task_numa_group(struct task_struct *p, int cpupid, int flags)

{

	struct numa_group *grp, *my_grp;

	struct task_struct *tsk;
@@ -1439,11 +1439,17 @@ static void task_numa_group(struct task_struct *p, int cpupid) 
	if (my_grp->nr_tasks == grp->nr_tasks && my_grp > grp)

		goto unlock;



	if (!get_numa_group(grp))

		goto unlock;

	/* 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;



	if (join && !get_numa_group(grp))

		join = false;



unlock:

	rcu_read_unlock();
@@ -1539,7 +1545,7 @@ void task_numa_fault(int last_cpupid, int node, int pages, int flags) 
	} else {

		priv = cpupid_match_pid(p, last_cpupid);

		if (!priv && !(flags & TNF_NO_GROUP))

			task_numa_group(p, last_cpupid);

			task_numa_group(p, last_cpupid, flags);

	}



	/*

mm/memory.c

+7 −0
Original line number Diff line number Diff line
@@ -3584,6 +3584,13 @@ int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma, 
	if (!pte_write(pte))

		flags |= TNF_NO_GROUP;



	/*

	 * Flag if the page is shared between multiple address spaces. This

	 * is later used when determining whether to group tasks together

	 */

	if (page_mapcount(page) > 1 && (vma->vm_flags & VM_SHARED))

		flags |= TNF_SHARED;



	last_cpupid = page_cpupid_last(page);

	page_nid = page_to_nid(page);

	target_nid = numa_migrate_prep(page, vma, addr, page_nid);