Commit 52bf84aa authored by Rik van Riel's avatar Rik van Riel Committed by Ingo Molnar
Browse files

sched/numa, mm: Remove p->numa_migrate_deferred 



Excessive migration of pages can hurt the performance of workloads
that span multiple NUMA nodes.  However, it turns out that the
p->numa_migrate_deferred knob is a really big hammer, which does
reduce migration rates, but does not actually help performance.

Now that the second stage of the automatic numa balancing code
has stabilized, it is time to replace the simplistic migration
deferral code with something smarter.

Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: Chegu Vinod <chegu_vinod@hp.com>
Link: http://lkml.kernel.org/r/1390860228-21539-2-git-send-email-riel@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent a57beec5

Documentation/sysctl/kernel.txt

+1 −9
Original line number Diff line number Diff line
@@ -386,8 +386,7 @@ feature should be disabled. Otherwise, if the system overhead from the 
feature is too high then the rate the kernel samples for NUMA hinting

faults may be controlled by the numa_balancing_scan_period_min_ms,

numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,

numa_balancing_scan_size_mb, numa_balancing_settle_count sysctls and

numa_balancing_migrate_deferred.

numa_balancing_scan_size_mb, and numa_balancing_settle_count sysctls.



==============================================================
@@ -428,13 +427,6 @@ rate for each task. 
numa_balancing_scan_size_mb is how many megabytes worth of pages are

scanned for a given scan.



numa_balancing_migrate_deferred is how many page migrations get skipped

unconditionally, after a page migration is skipped because a page is shared

with other tasks. This reduces page migration overhead, and determines

how much stronger the "move task near its memory" policy scheduler becomes,

versus the "move memory near its task" memory management policy, for workloads

with shared memory.



==============================================================



osrelease, ostype & version:

include/linux/sched.h

+0 −1
Original line number Diff line number Diff line
@@ -1457,7 +1457,6 @@ struct task_struct { 
	unsigned int numa_scan_period;

	unsigned int numa_scan_period_max;

	int numa_preferred_nid;

	int numa_migrate_deferred;

	unsigned long numa_migrate_retry;

	u64 node_stamp;			/* migration stamp  */

	struct callback_head numa_work;

kernel/sched/fair.c

+0 −8
Original line number Diff line number Diff line
@@ -819,14 +819,6 @@ 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;



/*

 * After skipping a page migration on a shared page, skip N more numa page

 * migrations unconditionally. This reduces the number of NUMA migrations

 * in shared memory workloads, and has the effect of pulling tasks towards

 * where their memory lives, over pulling the memory towards the task.

 */

unsigned int sysctl_numa_balancing_migrate_deferred = 16;



static unsigned int task_nr_scan_windows(struct task_struct *p)

{

	unsigned long rss = 0;

kernel/sysctl.c

+0 −7
Original line number Diff line number Diff line
@@ -384,13 +384,6 @@ static struct ctl_table kern_table[] = { 
		.mode		= 0644,

		.proc_handler	= proc_dointvec,

	},

	{

		.procname       = "numa_balancing_migrate_deferred",

		.data           = &sysctl_numa_balancing_migrate_deferred,

		.maxlen         = sizeof(unsigned int),

		.mode           = 0644,

		.proc_handler   = proc_dointvec,

	},

#endif /* CONFIG_NUMA_BALANCING */

#endif /* CONFIG_SCHED_DEBUG */

	{

mm/mempolicy.c

+0 −45
Original line number Diff line number Diff line
@@ -2304,35 +2304,6 @@ static void sp_free(struct sp_node *n) 
	kmem_cache_free(sn_cache, n);

}



#ifdef CONFIG_NUMA_BALANCING

static bool numa_migrate_deferred(struct task_struct *p, int last_cpupid)

{

	/* Never defer a private fault */

	if (cpupid_match_pid(p, last_cpupid))

		return false;



	if (p->numa_migrate_deferred) {

		p->numa_migrate_deferred--;

		return true;

	}

	return false;

}



static inline void defer_numa_migrate(struct task_struct *p)

{

	p->numa_migrate_deferred = sysctl_numa_balancing_migrate_deferred;

}

#else

static inline bool numa_migrate_deferred(struct task_struct *p, int last_cpupid)

{

	return false;

}



static inline void defer_numa_migrate(struct task_struct *p)

{

}

#endif /* CONFIG_NUMA_BALANCING */



/**

 * mpol_misplaced - check whether current page node is valid in policy

 *
@@ -2435,24 +2406,8 @@ int mpol_misplaced(struct page *page, struct vm_area_struct *vma, unsigned long 
		 */

		last_cpupid = page_cpupid_xchg_last(page, this_cpupid);

		if (!cpupid_pid_unset(last_cpupid) && cpupid_to_nid(last_cpupid) != thisnid) {



			/* See sysctl_numa_balancing_migrate_deferred comment */

			if (!cpupid_match_pid(current, last_cpupid))

				defer_numa_migrate(current);



			goto out;

		}



		/*

		 * The quadratic filter above reduces extraneous migration

		 * of shared pages somewhat. This code reduces it even more,

		 * reducing the overhead of page migrations of shared pages.

		 * This makes workloads with shared pages rely more on

		 * "move task near its memory", and less on "move memory

		 * towards its task", which is exactly what we want.

		 */

		if (numa_migrate_deferred(current, last_cpupid))

			goto out;

	}



	if (curnid != polnid)

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