[Devel] [PATCH RHEL7 COMMIT] mm/vmscan: scan active file and anon lists if inactive file list is too short

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-957.10.1.vz7.85.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-957.10.1.vz7.85.7
------>
commit d742225d792a285e92ea982b8e0d9511f87ddc44
Author: Andrey Ryabinin <aryabinin at virtuozzo.com>
Date:   Fri Mar 29 16:44:42 2019 +0300

    mm/vmscan: scan active file and anon lists if inactive file list is too short
    
    ltp test mm.mtest01w fails: it just tries to allocate and use 80% of
    available RAM+swap which is > RAMSIZE, so swap is intended to be used.
    
    Instead the test process is killed by OOM:
    get_scan_count() detects that cgroup has enough inactive file to reclaim
    only it and does not touch active anon.
    (inactive_file_low == false, as the test does not generate pagecache at
    all and there are several entries in inactive pagecache (1-10) which we
    cann't reclaim, they are activated instead).
    
    Thus active lists are not reclaimed => active anon (plenty of it) is not
    reclaimed (swapped out), reclaim is unsuccessful => OOM.
    
    How we fix this:
    1) we honor absolute value of inactive file cache:
       scan_balance is set to SCAN_FILE only in case
       inactive file is > 4Mb.
       And don't decrease (with sc->priority increase) the size of required
       inactive file cache when make a descision to scan file cache only.
    
    2) the above leads to "has_inactive" is set only if
       inactive file is > 4Mb.
    
    3) if we did not reclaim anything while processing inactive file,
       shrink active lists as well.
    
    https://jira.sw.ru/browse/PSBM-92480
    
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
    Acked-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 mm/vmscan.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a122e4cfa1a4..d84ba1a5c4f8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2208,9 +2208,11 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
 	/*
 	 * There is enough inactive page cache, do not reclaim
 	 * anything from the anonymous working set right now.
+	 * We don't decrease the required level of inactive page cache
+	 * with sc->priority decrease.
 	 */
 	if (!inactive_file_low &&
-	    lruvec_lru_size(lruvec, LRU_INACTIVE_FILE) >> sc->priority) {
+	    lruvec_lru_size(lruvec, LRU_INACTIVE_FILE) >> (DEF_PRIORITY - 2)) {
 		scan_balance = SCAN_FILE;
 		goto out;
 	}
@@ -2262,7 +2264,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
 	fraction[1] = fp;
 	denominator = ap + fp + 1;
 out:
-	sc->has_inactive = !inactive_file_low ||
+	sc->has_inactive = (!inactive_file_low && (scan_balance == SCAN_FILE)) ||
 		((scan_balance != SCAN_FILE) && !inactive_anon_low);
 	*lru_pages = 0;
 	for_each_evictable_lru(lru) {
@@ -2597,7 +2599,8 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc,
 			}
 		} while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
 
-		if (!sc->has_inactive && !sc->may_shrink_active) {
+		if ((!sc->has_inactive || !sc->nr_reclaimed)
+		    && !sc->may_shrink_active) {
 			sc->may_shrink_active = 1;
 			retry = true;
 			continue;