[PATCH] mm/compaction : do optimazition when the migration scanner gets no page

[PATCH] mm/compaction : do optimazition when the migration scanner gets no page

[Huang Shijie]

In the real tests, there are maybe many times the cc->nr_migratepages is zero,
but isolate_migratepages() returns ISOLATE_SUCCESS.
In order to get better performance, we should check the number of the
really isolated pages. And do the optimazition for this case.

Also fix the confused comments(from Mel Gorman).

Tested this patch in MX6Q board.

Signed-off-by: Huang Shijie <b32955@freescale.com>
---
 mm/compaction.c |   28 ++++++++++++++++------------
 1 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index bf8e8b2..b40d904 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -246,8 +246,8 @@ static bool too_many_isolated(struct zone *zone)
 /* possible outcome of isolate_migratepages */
 typedef enum {
 	ISOLATE_ABORT,		/* Abort compaction now */
-	ISOLATE_NONE,		/* No pages isolated, continue scanning */
-	ISOLATE_SUCCESS,	/* Pages isolated, migrate */
+	ISOLATE_NONE,		/* No pages scanned, consider next pageblock*/
+	ISOLATE_SUCCESS,	/* Pages scanned and maybe isolated, migrate */
 } isolate_migrate_t;
 
 /*
@@ -540,7 +540,7 @@ 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;
+		int err = 0;
 
 		switch (isolate_migratepages(zone, cc)) {
 		case ISOLATE_ABORT:
@@ -552,17 +552,21 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
 			;
 		}
 
-		nr_migrate = cc->nr_migratepages;
-		err = migrate_pages(&cc->migratepages, compaction_alloc,
-				(unsigned long)cc, false,
-				cc->sync);
-		update_nr_listpages(cc);
-		nr_remaining = cc->nr_migratepages;
+		nr_migrate = nr_remaining = cc->nr_migratepages;
+		if (nr_migrate) {
+			err = migrate_pages(&cc->migratepages, compaction_alloc,
+					(unsigned long)cc, false,
+					cc->sync);
+			update_nr_listpages(cc);
+			nr_remaining = cc->nr_migratepages;
+			count_vm_events(COMPACTPAGES,
+					nr_migrate - nr_remaining);
+			if (nr_remaining)
+				count_vm_events(COMPACTPAGEFAILED,
+						nr_remaining);
+		}
 
 		count_vm_event(COMPACTBLOCKS);
-		count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
-		if (nr_remaining)
-			count_vm_events(COMPACTPAGEFAILED, nr_remaining);
 		trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
 						nr_remaining);
 
-- 
1.7.3.2


--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH] mm/compaction : do optimazition when the migration scanner gets no page

[Mel Gorman]

On Fri, Jan 06, 2012 at 12:57:41PM +0800, Huang Shijie wrote:
> In the real tests, there are maybe many times the cc->nr_migratepages is zero,
> but isolate_migratepages() returns ISOLATE_SUCCESS.

Odd choice of language. Are there or are there not many times that
cc->nr_migratepages is zero? It does not affect the patch but it is
a slightly confusing changelog.

> In order to get better performance, we should check the number of the
> really isolated pages. And do the optimazition for this case.
> 

It's not critical for this patch but in the future it is preferred if
the performance impact can be quantified if that is your justification
for merging. I would expect the performance impact of this patch to
be marginal.

> Also fix the confused comments(from Mel Gorman).
> 
> Tested this patch in MX6Q board.
> 
> Signed-off-by: Huang Shijie <b32955@freescale.com>

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>