Commit 0a647f38 authored Jul 03, 2013 by Cody P Schafer Committed by Linus Torvalds Jul 03, 2013

mm/page_alloc: convert zone_pcp_update() to rely on memory barriers instead of stop_machine()



zone_pcp_update()'s goal is to adjust the ->high and ->mark members of a
percpu pageset based on a zone's ->managed_pages.  We don't need to drain
the entire percpu pageset just to modify these fields.

This lets us avoid calling setup_pageset() (and the draining required to
call it) and instead allows simply setting the fields' values (with some
attention paid to memory barriers to prevent the relationship between
->batch and ->high from being thrown off).

This does change the behavior of zone_pcp_update() as the percpu pagesets
will not be drained when zone_pcp_update() is called (they will end up
being shrunk, not completely drained, later when a 0-order page is freed
in free_hot_cold_page()).

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Cc: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 998d39cb

mm/page_alloc.c

+9 −24

Original line number	Diff line number	Diff line
		@@ -6085,33 +6085,18 @@ void free_contig_range(unsigned long pfn, unsigned nr_pages)
		#endif

		#ifdef CONFIG_MEMORY_HOTPLUG
		static int __meminit __zone_pcp_update(void *data)
		{
		struct zone *zone = data;
		int cpu;
		unsigned long batch = zone_batchsize(zone), flags;

		for_each_possible_cpu(cpu) {
		struct per_cpu_pageset *pset;
		struct per_cpu_pages *pcp;

		pset = per_cpu_ptr(zone->pageset, cpu);
		pcp = &pset->pcp;

		local_irq_save(flags);
		if (pcp->count > 0)
		free_pcppages_bulk(zone, pcp->count, pcp);
		drain_zonestat(zone, pset);
		setup_pageset(pset, batch);
		local_irq_restore(flags);
		}
		return 0;
		}

		/*
		* The zone indicated has a new number of managed_pages; batch sizes and percpu
		* page high values need to be recalulated.
		*/
		void __meminit zone_pcp_update(struct zone *zone)
		{
		unsigned cpu;
		unsigned long batch;
		mutex_lock(&pcp_batch_high_lock);
		stop_machine(__zone_pcp_update, zone, NULL);
		batch = zone_batchsize(zone);
		for_each_possible_cpu(cpu)
		pageset_set_batch(per_cpu_ptr(zone->pageset, cpu), batch);
		mutex_unlock(&pcp_batch_high_lock);
		}
		#endif

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