[RESEND PATCH 3/3] mm/vmscan: make several optimizations for isolate_lru_pages()

[qiwuchen55@xxxxxxxxx]

From: chenqiwu <chenqiwu@xxxxxxxxxx>

1) Simplify the code of initializing some variables.
1) Constify the LRU isolation mode.
2) Define a page_zoneidx variable to reduce the redundant code
of page_zonenum().

Signed-off-by: chenqiwu <chenqiwu@xxxxxxxxxx>
---
 mm/vmscan.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b06868f..2f65a91 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1638,16 +1638,15 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 	struct list_head *src = &lruvec->lists[lru];
 	unsigned long nr_taken = 0;
 	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
-	unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
+	unsigned long nr_skipped[MAX_NR_ZONES] = { 0 };
 	unsigned long skipped = 0;
-	unsigned long scan, total_scan, nr_pages;
+	unsigned long scan = 0, total_scan = 0, nr_pages;
 	LIST_HEAD(pages_skipped);
-	isolate_mode_t mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED);
+	const isolate_mode_t mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED);
 
-	total_scan = 0;
-	scan = 0;
 	while (scan < nr_to_scan && !list_empty(src)) {
 		struct page *page;
+		enum zone_type page_zoneidx;
 
 		page = lru_to_page(src);
 		prefetchw_prev_lru_page(page, src, flags);
@@ -1657,9 +1656,10 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		nr_pages = compound_nr(page);
 		total_scan += nr_pages;
 
-		if (page_zonenum(page) > sc->reclaim_idx) {
+		page_zoneidx = page_zonenum(page);
+		if (page_zoneidx > sc->reclaim_idx) {
 			list_move(&page->lru, &pages_skipped);
-			nr_skipped[page_zonenum(page)] += nr_pages;
+			nr_skipped[page_zoneidx] += nr_pages;
 			continue;
 		}
 
@@ -1677,7 +1677,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		switch (__isolate_lru_page(page, mode)) {
 		case 0:
 			nr_taken += nr_pages;
-			nr_zone_taken[page_zonenum(page)] += nr_pages;
+			nr_zone_taken[page_zoneidx] += nr_pages;
 			list_move(&page->lru, dst);
 			break;
 
-- 
1.9.1