[RFC][PATCH v2 5/8] Don't deactivate the page if trylock_page() is failed.

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

Currently, wipe_page_reference() increment refctx->referenced variable
if trylock_page() is failed. but it is meaningless at all.
shrink_active_list() deactivate the page although the page was
referenced. The page shouldn't be deactivated with young bit. it
break reclaim basic theory and decrease reclaim throughput.

This patch introduce new SWAP_AGAIN return value to
wipe_page_reference().

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
---
 mm/rmap.c   |    5 ++++-
 mm/vmscan.c |   15 +++++++++++++--
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 2f4451b..b84f350 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -539,6 +539,9 @@ static int wipe_page_reference_file(struct page *page,
  *
  * Quick test_and_clear_referenced for all mappings to a page,
  * returns the number of ptes which referenced the page.
+ *
+ * SWAP_SUCCESS  - success to wipe all ptes
+ * SWAP_AGAIN    - temporary busy, try again later
  */
 int wipe_page_reference(struct page *page,
 			struct mem_cgroup *memcg,
@@ -555,7 +558,7 @@ int wipe_page_reference(struct page *page,
 		    (!PageAnon(page) || PageKsm(page))) {
 			we_locked = trylock_page(page);
 			if (!we_locked) {
-				refctx->referenced++;
+				ret = SWAP_AGAIN;
 				goto out;
 			}
 		}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c59baa9..a01cf5e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -577,6 +577,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		struct address_space *mapping;
 		struct page *page;
 		int may_enter_fs;
+		int ret;
 		struct page_reference_context refctx = {
 			.is_page_locked = 1,
 		};
@@ -621,7 +622,11 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				goto keep_locked;
 		}
 
-		wipe_page_reference(page, sc->mem_cgroup, &refctx);
+		ret = wipe_page_reference(page, sc->mem_cgroup, &refctx);
+		if (ret == SWAP_AGAIN)
+			goto keep_locked;
+		VM_BUG_ON(ret != SWAP_SUCCESS);
+
 		/*
 		 * In active use or really unfreeable?  Activate it.
 		 * If page which have PG_mlocked lost isoltation race,
@@ -1321,6 +1326,7 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
 	spin_unlock_irq(&zone->lru_lock);
 
 	while (!list_empty(&l_hold)) {
+		int ret;
 		struct page_reference_context refctx = {
 			.is_page_locked = 0,
 		};
@@ -1340,7 +1346,12 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
 			continue;
 		}
 
-		wipe_page_reference(page, sc->mem_cgroup, &refctx);
+		ret = wipe_page_reference(page, sc->mem_cgroup, &refctx);
+		if (ret == SWAP_AGAIN) {
+			list_add(&page->lru, &l_active);
+			continue;
+		}
+		VM_BUG_ON(ret != SWAP_SUCCESS);
 
 		if (refctx.referenced)
 			nr_rotated++;
-- 
1.6.5.2



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