Commit dbe2d4e4 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
Browse files

mm, compaction: round-robin the order while searching the free lists for a target 

As compaction proceeds and creates high-order blocks, the free list
search gets less efficient as the larger blocks are used as compaction
targets.  Eventually, the larger blocks will be behind the migration
scanner for partially migrated pageblocks and the search fails.  This
patch round-robins what orders are searched so that larger blocks can be
ignored and find smaller blocks that can be used as migration targets.

The overall impact was small on 1-socket but it avoids corner cases
where the migration/free scanners meet prematurely or situations where
many of the pageblocks encountered by the free scanner are almost full
instead of being properly packed.  Previous testing had indicated that
without this patch there were occasional large spikes in the free
scanner without this patch.

[dan.carpenter@oracle.com: fix static checker warning]
Link: http://lkml.kernel.org/r/20190118175136.31341-20-mgorman@techsingularity.net


Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d097a6f6

mm/compaction.c

+30 −3
Original line number Diff line number Diff line
@@ -1147,6 +1147,24 @@ fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long 
		set_pageblock_skip(page);

}



/* Search orders in round-robin fashion */

static int next_search_order(struct compact_control *cc, int order)

{

	order--;

	if (order < 0)

		order = cc->order - 1;



	/* Search wrapped around? */

	if (order == cc->search_order) {

		cc->search_order--;

		if (cc->search_order < 0)

			cc->search_order = cc->order - 1;

		return -1;

	}



	return order;

}



static unsigned long

fast_isolate_freepages(struct compact_control *cc)

{
@@ -1183,9 +1201,15 @@ fast_isolate_freepages(struct compact_control *cc) 
	if (WARN_ON_ONCE(min_pfn > low_pfn))

		low_pfn = min_pfn;



	for (order = cc->order - 1;

	     order >= 0 && !page;

	     order--) {

	/*

	 * Search starts from the last successful isolation order or the next

	 * order to search after a previous failure

	 */

	cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order);



	for (order = cc->search_order;

	     !page && order >= 0;

	     order = next_search_order(cc, order)) {

		struct free_area *area = &cc->zone->free_area[order];

		struct list_head *freelist;

		struct page *freepage;
@@ -1209,6 +1233,7 @@ fast_isolate_freepages(struct compact_control *cc) 


			if (pfn >= low_pfn) {

				cc->fast_search_fail = 0;

				cc->search_order = order;

				page = freepage;

				break;

			}
@@ -2138,6 +2163,7 @@ static enum compact_result compact_zone_order(struct zone *zone, int order, 
		.total_migrate_scanned = 0,

		.total_free_scanned = 0,

		.order = order,

		.search_order = order,

		.gfp_mask = gfp_mask,

		.zone = zone,

		.mode = (prio == COMPACT_PRIO_ASYNC) ?
@@ -2369,6 +2395,7 @@ static void kcompactd_do_work(pg_data_t *pgdat) 
	struct zone *zone;

	struct compact_control cc = {

		.order = pgdat->kcompactd_max_order,

		.search_order = pgdat->kcompactd_max_order,

		.total_migrate_scanned = 0,

		.total_free_scanned = 0,

		.classzone_idx = pgdat->kcompactd_classzone_idx,

mm/internal.h

+2 −1
Original line number Diff line number Diff line
@@ -192,7 +192,8 @@ struct compact_control { 
	struct zone *zone;

	unsigned long total_migrate_scanned;

	unsigned long total_free_scanned;

	unsigned int fast_search_fail;	/* failures to use free list searches */

	unsigned short fast_search_fail;/* failures to use free list searches */

	short search_order;		/* order to start a fast search at */

	const gfp_t gfp_mask;		/* gfp mask of a direct compactor */

	int order;			/* order a direct compactor needs */

	int migratetype;		/* migratetype of direct compactor */

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