On Wed, Jun 22, 2016 at 04:04:34PM +0200, Vlastimil Babka wrote:

quoted

-static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
+static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc,
+		enum zone_type classzone_idx)
{
	struct zoneref *z;
	struct zone *zone;
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
	gfp_t orig_mask;
-	enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);

	/*
	 * If the number of buffer_heads in the machine exceeds the maximum

@@ -2560,15 +2579,20 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)

	for_each_zone_zonelist_nodemask(zone, z, zonelist,
					gfp_zone(sc->gfp_mask), sc->nodemask) {

Using sc->reclaim_idx could be faster/nicer here than gfp_zone()?

Yes, then the reclaim_idx and classzone_idx needs to be updated if
buffer_heads_over_limit in the check above but that is better anyway.

Although after "mm, vmscan: Update classzone_idx if buffer_heads_over_limit"
there would need to be a variable for the highmem adjusted value - maybe
reuse "requested_highidx"? Not important though.

I think it's ok in the buffer_heads_over_limit case to reclaim
from more zones than requested. It may require another pass through
do_try_to_free_pages if a low zone was not reclaimed and required by the
caller but that's ok and expected if there are too many buffer_heads.

quoted

-		enum zone_type classzone_idx;
-
		if (!populated_zone(zone))
			continue;

-		classzone_idx = requested_highidx;
+		/*
+		 * Note that reclaim_idx does not change as it is the highest
+		 * zone reclaimed from which for empty zones is a no-op but
+		 * classzone_idx is used by shrink_node to test if the slabs
+		 * should be shrunk on a given node.
+		 */
		while (!populated_zone(zone->zone_pgdat->node_zones +
-							classzone_idx))
+							classzone_idx)) {
			classzone_idx--;
+			continue;
+		}

		/*
		 * Take care memory controller reclaiming has small influence

@@ -2594,8 +2618,8 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)

			 */
			if (IS_ENABLED(CONFIG_COMPACTION) &&
			    sc->order > PAGE_ALLOC_COSTLY_ORDER &&
-			    zonelist_zone_idx(z) <= requested_highidx &&
-			    compaction_ready(zone, sc->order, requested_highidx)) {
+			    zonelist_zone_idx(z) <= classzone_idx &&
+			    compaction_ready(zone, sc->order, classzone_idx)) {
				sc->compaction_ready = true;
				continue;
			}

@@ -2615,7 +2639,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)

			/* need some check for avoid more shrink_zone() */
		}

-		shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
+		shrink_node(zone->zone_pgdat, sc, classzone_idx);
	}

	/*

@@ -2647,6 +2671,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,

	int initial_priority = sc->priority;
	unsigned long total_scanned = 0;
	unsigned long writeback_threshold;
+	enum zone_type classzone_idx = sc->reclaim_idx;

Hmm, try_to_free_mem_cgroup_pages() seems to call this with sc->reclaim_idx
not explicitly inirialized (e.g. 0). And shrink_all_memory() as well. I
probably didn't check them in v6 and pointed out only try_to_free_pages()
(which is now OK), sorry.

That gets fixed in "mm, memcg: move memcg limit enforcement from zones
to nodes" but I can move the hunk to this patch to make bisection a
little easier.

quoted

retry:
	delayacct_freepages_start();

@@ -2657,7 +2682,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,

		vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
				sc->priority);
		sc->nr_scanned = 0;
-		shrink_zones(zonelist, sc);
+		shrink_zones(zonelist, sc, classzone_idx);

Looks like classzone_idx here is only used here to pass to shrink_zones()
unchanged, which means it can just use it directly without a new param?

Yes

-- 
Mel Gorman
SUSE Labs

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