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

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 <>
Reviewed-by: default avatarNaoya Horiguchi <>
Cc: Minchan Kim <>
Cc: Mel Gorman <>
Cc: Joonsoo Kim <>
Cc: Bartlomiej Zolnierkiewicz <>
Acked-by: default avatarMichal Nazarewicz <>
Cc: Christoph Lameter <>
Cc: Rik van Riel <>
Acked-by: default avatarDavid Rientjes <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent aeef4b83
......@@ -5,6 +5,7 @@
#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,
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),
__field(unsigned long, nr_migrated)
......@@ -58,7 +60,22 @@ TRACE_EVENT(mm_compaction_migratepages,
__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;
list_for_each(page_lru, migratepages)
__entry->nr_migrated = nr_all - nr_failed;
__entry->nr_failed = nr_failed;
......@@ -822,22 +822,6 @@ static void compaction_free(struct page *page, unsigned long data)
* 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)
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)
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)
err = migrate_pages(&cc->migratepages, compaction_alloc,
compaction_free, (unsigned long)cc, cc->mode,
nr_remaining = cc->nr_migratepages;
trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
trace_mm_compaction_migratepages(cc->nr_migratepages, err,
/* Release isolated pages not migrated */
/* All pages were either migrated or will be released */
cc->nr_migratepages = 0;
if (err) {
cc->nr_migratepages = 0;
* migrate_pages() may return -ENOMEM when scanners meet
* and we want compact_finished() to detect it
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