mm/compaction: do not count migratepages when unnecessary

commit f8c9301fa5a2a8b873c67f2a3d8230d5c13f61b7 upstream.

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: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Naoya 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: Michal Nazarewicz <mina86@mina86.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
index 06f544e..c6814b9 100644 (file)
--- a/include/trace/events/compaction.h
+++ b/include/trace/events/compaction.h
@@ -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;
        ),
 

diff --git a/mm/compaction.c b/mm/compaction.c
index 4d38c85..d85ca94 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -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