Commit 943dca1a authored Jan 21, 2014 by Yasuaki Ishimatsu Committed by Linus Torvalds Jan 21, 2014

mm: get rid of unnecessary pageblock scanning in setup_zone_migrate_reserve

Yasuaki Ishimatsu reported memory hot-add spent more than 5 _hours_ on
9TB memory machine since onlining memory sections is too slow.  And we
found out setup_zone_migrate_reserve spent >90% of the time.

The problem is, setup_zone_migrate_reserve scans all pageblocks
unconditionally, but it is only necessary if the number of reserved
block was reduced (i.e.  memory hot remove).

Moreover, maximum MIGRATE_RESERVE per zone is currently 2.  It means
that the number of reserved pageblocks is almost always unchanged.

This patch adds zone->nr_migrate_reserve_block to maintain the number of
MIGRATE_RESERVE pageblocks and it reduces the overhead of
setup_zone_migrate_reserve dramatically.  The following table shows time
of onlining a memory section.

  Amount of memory     | 128GB | 192GB | 256GB|
  ---------------------------------------------
  linux-3.12           |  23.9 |  31.4 | 44.5 |
  This patch           |   8.3 |   8.3 |  8.6 |
  Mel's proposal patch |  10.9 |  19.2 | 31.3 |
  ---------------------------------------------
                                   (millisecond)

  128GB : 4 nodes and each node has 32GB of memory
  192GB : 6 nodes and each node has 32GB of memory
  256GB : 8 nodes and each node has 32GB of memory

  (*1) Mel proposed his idea by the following threads.
       https://lkml.org/lkml/2013/10/30/272



[akpm@linux-foundation.org: tweak comment]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Reported-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Tested-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 34e431b0

include/linux/mmzone.h

+6 −0

Original line number	Diff line number	Diff line
		@@ -489,6 +489,12 @@ struct zone {
		unsigned long present_pages;
		unsigned long managed_pages;

		/*
		* Number of MIGRATE_RESEVE page block. To maintain for just
		* optimization. Protected by zone->lock.
		*/
		int nr_migrate_reserve_block;

		/*
		* rarely used fields:
		*/

mm/page_alloc.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -3901,6 +3901,7 @@ static void setup_zone_migrate_reserve(struct zone *zone)
		struct page *page;
		unsigned long block_migratetype;
		int reserve;
		int old_reserve;

		/*
		* Get the start pfn, end pfn and the number of blocks to reserve
		@@ -3922,6 +3923,12 @@ static void setup_zone_migrate_reserve(struct zone *zone)
		* future allocation of hugepages at runtime.
		*/
		reserve = min(2, reserve);
		old_reserve = zone->nr_migrate_reserve_block;

		/* When memory hot-add, we almost always need to do nothing */
		if (reserve == old_reserve)
		return;
		zone->nr_migrate_reserve_block = reserve;

		for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
		if (!pfn_valid(pfn))
		@@ -3959,6 +3966,12 @@ static void setup_zone_migrate_reserve(struct zone *zone)
		reserve--;
		continue;
		}
		} else if (!old_reserve) {
		/*
		* At boot time we don't need to scan the whole zone
		* for turning off MIGRATE_RESERVE.
		*/
		break;
		}

		/*

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