[Devel] [PATCH RHEL7 COMMIT] Revert "mm: vmscan: do not scan lruvec if it seems to be unreclaimable"

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-229.7.2.vz7.9.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-229.7.2.vz7.9.25
------>
commit c118c74c7ff35759a4f1491041fea2284fd49feb
Author: Vladimir Davydov <vdavydov at virtuozzo.com>
Date:   Fri Jan 22 19:16:43 2016 +0400

    Revert "mm: vmscan: do not scan lruvec if it seems to be unreclaimable"
    
    This reverts commit 92dd01fd61017f4efc7819bc5f5711981dcd6a88.
    
    The patch being reverted was introduced in order to fix PSBM-35155. At
    that time I used memory.high to avoid kmem allocation failures - it was
    set by vcmmd to be several percent less than memory.limit, so that there
    should almost always be some gap between limit and usage for a container
    to grow its memory before hitting OOM. In fact, this was kinda abusing
    memory.high. The whole point of memory.high is avoiding OOM, so it
    shouldn't be unexpected at all that OOM was delayed by orders of
    magnitude if memory.high was set. So I introduced this heuristic to make
    OOM happen earlier even if memory.high is set below memory.limit.
    
    This workaround had a downside - it resulted in premature OOM, which
    spuriously failed our tests. Nowadays, I don't use memory.high as a
    protection against kmem allocation failures - I just never fail them.
    So revert the workaround.
    
    Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
---
 include/linux/mmzone.h |  1 -
 mm/swap.c              |  1 -
 mm/vmscan.c            | 23 -----------------------
 3 files changed, 25 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index faf3c96..abe7110 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -211,7 +211,6 @@ struct zone_reclaim_stat {
 struct lruvec {
 	struct list_head lists[NR_LRU_LISTS];
 	struct zone_reclaim_stat reclaim_stat;
-	unsigned long pages_scanned;
 #ifdef CONFIG_MEMCG
 	struct zone *zone;
 #endif
diff --git a/mm/swap.c b/mm/swap.c
index 68dd289..0a42ebf 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -61,7 +61,6 @@ static void __page_cache_release(struct page *page)
 		VM_BUG_ON_PAGE(!PageLRU(page), page);
 		__ClearPageLRU(page);
 		del_page_from_lru_list(page, lruvec, page_off_lru(page));
-		lruvec->pages_scanned = 0;
 		spin_unlock_irqrestore(&zone->lru_lock, flags);
 	}
 }
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3b96a02..0406c11 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -178,20 +178,6 @@ static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
 	return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
 }
 
-static bool lruvec_reclaimable(struct lruvec *lruvec, bool may_swap)
-{
-	unsigned long reclaimable;
-
-	reclaimable = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
-		      get_lru_size(lruvec, LRU_INACTIVE_FILE);
-
-	if (may_swap && get_nr_swap_pages() > 0)
-		reclaimable += get_lru_size(lruvec, LRU_ACTIVE_ANON) +
-			       get_lru_size(lruvec, LRU_INACTIVE_ANON);
-
-	return lruvec->pages_scanned < reclaimable * 6;
-}
-
 /*
  * Add a shrinker callback to be called from the vm.
  */
@@ -1543,7 +1529,6 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 	__mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
 	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
 
-	lruvec->pages_scanned += nr_scanned;
 	if (global_reclaim(sc)) {
 		zone->pages_scanned += nr_scanned;
 		if (current_is_kswapd())
@@ -1563,9 +1548,6 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 
 	spin_lock_irq(&zone->lru_lock);
 
-	if (nr_reclaimed)
-		lruvec->pages_scanned = 0;
-
 	reclaim_stat->recent_scanned[file] += nr_taken;
 
 	if (global_reclaim(sc)) {
@@ -1739,7 +1721,6 @@ static void shrink_active_list(unsigned long nr_to_scan,
 
 	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
 				     &nr_scanned, sc, isolate_mode, lru);
-	lruvec->pages_scanned += nr_scanned;
 	if (global_reclaim(sc))
 		zone->pages_scanned += nr_scanned;
 
@@ -2376,10 +2357,6 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc,
 				continue;
 
 			lruvec = mem_cgroup_zone_lruvec(zone, memcg);
-			if (!global_reclaim(sc) &&
-			    !lruvec_reclaimable(lruvec, sc->may_swap))
-				continue;
-
 			scanned = sc->nr_scanned;
 
 			shrink_lruvec(lruvec, sc, &lru_pages);