[PATCH 5/5] mm: vmscan: move dirty pages out of the way until they're flushed

[Johannes Weiner]

We noticed a performance regression when moving hadoop workloads from
3.10 kernels to 4.0 and 4.6. This is accompanied by increased pageout
activity initiated by kswapd as well as frequent bursts of allocation
stalls and direct reclaim scans. Even lowering the dirty ratios to the
equivalent of less than 1% of memory would not eliminate the issue,
suggesting that dirty pages concentrate where the scanner is looking.

This can be traced back to recent efforts of thrash avoidance. Where
3.10 would not detect refaulting pages and continuously supply clean
cache to the inactive list, a thrashing workload on 4.0+ will detect
and activate refaulting pages right away, distilling used-once pages
on the inactive list much more effectively. This is by design, and it
makes sense for clean cache. But for the most part our workload's
cache faults are refaults and its use-once cache is from streaming
writes. We end up with most of the inactive list dirty, and we don't
go after the active cache as long as we have use-once pages around.

But waiting for writes to avoid reclaiming clean cache that *might*
refault is a bad trade-off. Even if the refaults happen, reads are
faster than writes. Before getting bogged down on writeback, reclaim
should first look at *all* cache in the system, even active cache.

To accomplish this, activate pages that have been dirty or under
writeback for two inactive LRU cycles. We know at this point that
there are not enough clean inactive pages left to satisfy memory
demand in the system. The pages are marked for immediate reclaim,
meaning they'll get moved back to the inactive LRU tail as soon as
they're written back and become reclaimable. But in the meantime, by
reducing the inactive list to only immediately reclaimable pages, we
allow the scanner to deactivate and refill the inactive list with
clean cache from the active list tail to guarantee forward progress.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 include/linux/mm_inline.h | 7 +++++++
 mm/swap.c                 | 9 +++++----
 mm/vmscan.c               | 6 +++---
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 41d376e7116d..e030a68ead7e 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -50,6 +50,13 @@ static __always_inline void add_page_to_lru_list(struct page *page,
 	list_add(&page->lru, &lruvec->lists[lru]);
 }
 
+static __always_inline void add_page_to_lru_list_tail(struct page *page,
+				struct lruvec *lruvec, enum lru_list lru)
+{
+	update_lru_size(lruvec, lru, page_zonenum(page), hpage_nr_pages(page));
+	list_add_tail(&page->lru, &lruvec->lists[lru]);
+}
+
 static __always_inline void del_page_from_lru_list(struct page *page,
 				struct lruvec *lruvec, enum lru_list lru)
 {
diff --git a/mm/swap.c b/mm/swap.c
index aabf2e90fe32..c4910f14f957 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -209,9 +209,10 @@ static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec,
 {
 	int *pgmoved = arg;
 
-	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
-		enum lru_list lru = page_lru_base_type(page);
-		list_move_tail(&page->lru, &lruvec->lists[lru]);
+	if (PageLRU(page) && !PageUnevictable(page)) {
+		del_page_from_lru_list(page, lruvec, page_lru(page));
+		ClearPageActive(page);
+		add_page_to_lru_list_tail(page, lruvec, page_lru(page));
 		(*pgmoved)++;
 	}
 }
@@ -235,7 +236,7 @@ static void pagevec_move_tail(struct pagevec *pvec)
  */
 void rotate_reclaimable_page(struct page *page)
 {
-	if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
+	if (!PageLocked(page) && !PageDirty(page) &&
 	    !PageUnevictable(page) && PageLRU(page)) {
 		struct pagevec *pvec;
 		unsigned long flags;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index df0fe0cc438e..947ab6f4db10 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1063,7 +1063,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			    PageReclaim(page) &&
 			    test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
 				nr_immediate++;
-				goto keep_locked;
+				goto activate_locked;
 
 			/* Case 2 above */
 			} else if (sane_reclaim(sc) ||
@@ -1081,7 +1081,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				 */
 				SetPageReclaim(page);
 				nr_writeback++;
-				goto keep_locked;
+				goto activate_locked;
 
 			/* Case 3 above */
 			} else {
@@ -1174,7 +1174,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
 				SetPageReclaim(page);
 
-				goto keep_locked;
+				goto activate_locked;
 			}
 
 			if (references == PAGEREF_RECLAIM_CLEAN)
-- 
2.11.0