Commit f8c9301f authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
Browse files

mm/compaction: do not count migratepages when unnecessary 



During compaction, update_nr_listpages() has been used to count remaining
non-migrated and free pages after a call to migrage_pages().  The
freepages counting has become unneccessary, and it turns out that
migratepages counting is also unnecessary in most cases.

The only situation when it's needed to count cc->migratepages is when
migrate_pages() returns with a negative error code.  Otherwise, the
non-negative return value is the number of pages that were not migrated,
which is exactly the count of remaining pages in the cc->migratepages
list.

Furthermore, any non-zero count is only interesting for the tracepoint of
mm_compaction_migratepages events, because after that all remaining
unmigrated pages are put back and their count is set to 0.

This patch therefore removes update_nr_listpages() completely, and changes
the tracepoint definition so that the manual counting is done only when
the tracepoint is enabled, and only when migrate_pages() returns a
negative error code.

Furthermore, migrate_pages() and the tracepoints won't be called when
there's nothing to migrate.  This potentially avoids some wasted cycles
and reduces the volume of uninteresting mm_compaction_migratepages events
where "nr_migrated=0 nr_failed=0".  In the stress-highalloc mmtest, this
was about 75% of the events.  The mm_compaction_isolate_migratepages event
is better for determining that nothing was isolated for migration, and
this one was just duplicating the info.

Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: default avatarMichal Nazarewicz <mina86@mina86.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent aeef4b83

include/trace/events/compaction.h

+21 −4
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ 
#define _TRACE_COMPACTION_H



#include <linux/types.h>

#include <linux/list.h>

#include <linux/tracepoint.h>

#include <trace/events/gfpflags.h>
@@ -47,10 +48,11 @@ DEFINE_EVENT(mm_compaction_isolate_template, mm_compaction_isolate_freepages, 


TRACE_EVENT(mm_compaction_migratepages,



	TP_PROTO(unsigned long nr_migrated,

		unsigned long nr_failed),

	TP_PROTO(unsigned long nr_all,

		int migrate_rc,

		struct list_head *migratepages),



	TP_ARGS(nr_migrated, nr_failed),

	TP_ARGS(nr_all, migrate_rc, migratepages),



	TP_STRUCT__entry(

		__field(unsigned long, nr_migrated)
@@ -58,7 +60,22 @@ TRACE_EVENT(mm_compaction_migratepages, 
	),



	TP_fast_assign(

		__entry->nr_migrated = nr_migrated;

		unsigned long nr_failed = 0;

		struct list_head *page_lru;



		/*

		 * migrate_pages() returns either a non-negative number

		 * with the number of pages that failed migration, or an

		 * error code, in which case we need to count the remaining

		 * pages manually

		 */

		if (migrate_rc >= 0)

			nr_failed = migrate_rc;

		else

			list_for_each(page_lru, migratepages)

				nr_failed++;



		__entry->nr_migrated = nr_all - nr_failed;

		__entry->nr_failed = nr_failed;

	),

mm/compaction.c

+7 −24
Original line number Diff line number Diff line
@@ -822,22 +822,6 @@ static void compaction_free(struct page *page, unsigned long data) 
	cc->nr_freepages++;

}



/*

 * We cannot control nr_migratepages fully when migration is running as

 * migrate_pages() has no knowledge of of compact_control.  When migration is

 * complete, we count the number of pages on the list by hand.

 */

static void update_nr_listpages(struct compact_control *cc)

{

	int nr_migratepages = 0;

	struct page *page;



	list_for_each_entry(page, &cc->migratepages, lru)

		nr_migratepages++;



	cc->nr_migratepages = nr_migratepages;

}



/* possible outcome of isolate_migratepages */

typedef enum {

	ISOLATE_ABORT,		/* Abort compaction now */
@@ -1032,7 +1016,6 @@ static int compact_zone(struct zone *zone, struct compact_control *cc) 
	migrate_prep_local();



	while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {

		unsigned long nr_migrate, nr_remaining;

		int err;



		switch (isolate_migratepages(zone, cc)) {
@@ -1047,20 +1030,20 @@ static int compact_zone(struct zone *zone, struct compact_control *cc) 
			;

		}



		nr_migrate = cc->nr_migratepages;

		if (!cc->nr_migratepages)

			continue;



		err = migrate_pages(&cc->migratepages, compaction_alloc,

				compaction_free, (unsigned long)cc, cc->mode,

				MR_COMPACTION);

		update_nr_listpages(cc);

		nr_remaining = cc->nr_migratepages;



		trace_mm_compaction_migratepages(nr_migrate - nr_remaining,

						nr_remaining);

		trace_mm_compaction_migratepages(cc->nr_migratepages, err,

							&cc->migratepages);



		/* Release isolated pages not migrated */

		/* All pages were either migrated or will be released */

		cc->nr_migratepages = 0;

		if (err) {

			putback_movable_pages(&cc->migratepages);

			cc->nr_migratepages = 0;

			/*

			 * migrate_pages() may return -ENOMEM when scanners meet

			 * and we want compact_finished() to detect it

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