[PATCH 2/6] mm/page_alloc: Track range of active PCP lists during bulk free

[Mel Gorman <mgorman@techsingularity.net>]

free_pcppages_bulk() frees pages in a round-robin fashion. Originally,
this was dealing only with migratetypes but storing high-order pages
means that there can be many more empty lists that are uselessly
checked. Track the minimum and maximum active pindex to reduce the
search space.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/page_alloc.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 08de32cfd9bb..85cc1fe8bcc5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1450,6 +1450,8 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 					struct per_cpu_pages *pcp)
 {
 	int pindex = 0;
+	int min_pindex = 0;
+	int max_pindex = NR_PCP_LISTS - 1;
 	int batch_free = 0;
 	int nr_freed = 0;
 	unsigned int order;
@@ -1475,13 +1477,20 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 		 */
 		do {
 			batch_free++;
-			if (++pindex == NR_PCP_LISTS)
-				pindex = 0;
+			if (++pindex > max_pindex)
+				pindex = min_pindex;
 			list = &pcp->lists[pindex];
-		} while (list_empty(list));
+			if (!list_empty(list))
+				break;
+
+			if (pindex == max_pindex)
+				max_pindex--;
+			if (pindex == min_pindex)
+				min_pindex++;
+		} while (1);
 
 		/* This is the only non-empty list. Free them all. */
-		if (batch_free == NR_PCP_LISTS)
+		if (batch_free >= max_pindex - min_pindex)
 			batch_free = count;
 
 		order = pindex_to_order(pindex);
-- 
2.31.1