The traditional zone reclaim code is scanning the per-zone LRU lists
during direct reclaim and kswapd, and the per-zone per-memory cgroup
LRU lists when reclaiming on behalf of a memory cgroup limit.

Subsequent patches will convert the traditional reclaim code to
reclaim exclusively from the per-memory cgroup LRU lists.  As a
result, using the predicate for which LRU list is scanned will no
longer be appropriate to tell global reclaim from limit reclaim.

This patch adds a global_reclaim() predicate to tell direct/kswapd
reclaim from memory cgroup limit reclaim and substitutes it in all
places where currently scanning_global_lru() is used for that.

Signed-off-by: Johannes Weiner <redacted>
---
 mm/vmscan.c |   60 +++++++++++++++++++++++++++++++++++-----------------------
 1 files changed, 36 insertions(+), 24 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7502726..354f125 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -153,9 +153,25 @@ static LIST_HEAD(shrinker_list);
 static DECLARE_RWSEM(shrinker_rwsem);
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
-#define scanning_global_lru(sc)	(!(sc)->mem_cgroup)
+static bool global_reclaim(struct scan_control *sc)
+{
+	return !sc->mem_cgroup;
+}
+
+static bool scanning_global_lru(struct scan_control *sc)
+{
+	return !sc->mem_cgroup;
+}
 #else
-#define scanning_global_lru(sc)	(1)
+static bool global_reclaim(struct scan_control *sc)
+{
+	return true;
+}
+
+static bool scanning_global_lru(struct scan_control *sc)
+{
+	return true;
+}
 #endif
 
 static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,

@@ -1011,7 +1027,7 @@ keep_lumpy:
 	 * back off and wait for congestion to clear because further reclaim
 	 * will encounter the same problem
 	 */
-	if (nr_dirty && nr_dirty == nr_congested && scanning_global_lru(sc))
+	if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
 		zone_set_flag(zone, ZONE_CONGESTED);
 
 	free_page_list(&free_pages);

@@ -1330,7 +1346,7 @@ static int too_many_isolated(struct zone *zone, int file,
 	if (current_is_kswapd())
 		return 0;
 
-	if (!scanning_global_lru(sc))
+	if (!global_reclaim(sc))
 		return 0;
 
 	if (file) {

@@ -1508,6 +1524,12 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
 	if (scanning_global_lru(sc)) {
 		nr_taken = isolate_pages_global(nr_to_scan, &page_list,
 			&nr_scanned, sc->order, reclaim_mode, zone, 0, file);
+	} else {
+		nr_taken = mem_cgroup_isolate_pages(nr_to_scan, &page_list,
+			&nr_scanned, sc->order, reclaim_mode, zone,
+			sc->mem_cgroup, 0, file);
+	}

+	if (global_reclaim(sc)) {
 		zone->pages_scanned += nr_scanned;
 		if (current_is_kswapd())
 			__count_zone_vm_events(PGSCAN_KSWAPD, zone,

@@ -1515,14 +1537,6 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
 		else
 			__count_zone_vm_events(PGSCAN_DIRECT, zone,
 					       nr_scanned);
-	} else {
-		nr_taken = mem_cgroup_isolate_pages(nr_to_scan, &page_list,
-			&nr_scanned, sc->order, reclaim_mode, zone,
-			sc->mem_cgroup, 0, file);
-		/*
-		 * mem_cgroup_isolate_pages() keeps track of
-		 * scanned pages on its own.
-		 */
 	}
 
 	if (nr_taken == 0) {

@@ -1647,18 +1661,16 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
 						&pgscanned, sc->order,
 						reclaim_mode, zone,
 						1, file);
-		zone->pages_scanned += pgscanned;
 	} else {
 		nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold,
 						&pgscanned, sc->order,
 						reclaim_mode, zone,
 						sc->mem_cgroup, 1, file);
-		/*
-		 * mem_cgroup_isolate_pages() keeps track of
-		 * scanned pages on its own.
-		 */
 	}