[Devel] [PATCH RHEL8 COMMIT] mm/vmscan.c: generalize shrink_slab() calls in shrink_node()

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-80.1.2.vz8.3.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-80.1.2.vz8.3.4
------>
commit 64272ed6c80ac08c8a6147a8fb8abd3ed24bcb3b
Author: Vladimir Davydov <vdavydov.dev at gmail.com>
Date:   Thu Apr 2 17:13:05 2020 +0300

    mm/vmscan.c: generalize shrink_slab() calls in shrink_node()
    
    The patch makes shrink_slab() be called for root_mem_cgroup in the same
    way as it's called for the rest of cgroups.  This simplifies the logic
    and improves the readability.
    
    [ktkhai at virtuozzo.com: wrote changelog]
    Link: http://lkml.kernel.org/r/153063068338.1818.11496084754797453962.stgit@localhost.localdomain
    Signed-off-by: Vladimir Davydov <vdavydov.dev at gmail.com>
    
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    
    Tested-by: Shakeel Butt <shakeelb at google.com>
    Cc: Al Viro <viro at zeniv.linux.org.uk>
    Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
    Cc: Chris Wilson <chris at chris-wilson.co.uk>
    Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
    Cc: Guenter Roeck <linux at roeck-us.net>
    Cc: "Huang, Ying" <ying.huang at intel.com>
    Cc: Johannes Weiner <hannes at cmpxchg.org>
    Cc: Josef Bacik <jbacik at fb.com>
    Cc: Li RongQing <lirongqing at baidu.com>
    Cc: Matthew Wilcox <willy at infradead.org>
    Cc: Matthias Kaehlcke <mka at chromium.org>
    Cc: Mel Gorman <mgorman at techsingularity.net>
    Cc: Michal Hocko <mhocko at kernel.org>
    Cc: Minchan Kim <minchan at kernel.org>
    Cc: Philippe Ombredanne <pombredanne at nexb.com>
    Cc: Roman Gushchin <guro at fb.com>
    Cc: Sahitya Tummala <stummala at codeaurora.org>
    Cc: Stephen Rothwell <sfr at canb.auug.org.au>
    Cc: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
    Cc: Thomas Gleixner <tglx at linutronix.de>
    Cc: Waiman Long <longman at redhat.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    (cherry picked from commit aeed1d325d429ac9699c4bf62d17156d60905519)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/vmscan.c | 21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 80fa2e8b873a..0395e910f424 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -595,10 +595,8 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
  * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
  * unaware shrinkers will receive a node id of 0 instead.
  *
- * @memcg specifies the memory cgroup to target. If it is not NULL,
- * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
- * objects from the memory cgroup specified. Otherwise, only unaware
- * shrinkers are called.
+ * @memcg specifies the memory cgroup to target. Unaware shrinkers
+ * are called only if it is the root cgroup.
  *
  * @priority is sc->priority, we take the number of objects and >> by priority
  * in order to get the scan target.
@@ -612,7 +610,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 	struct shrinker *shrinker;
 	unsigned long freed = 0;
 
-	if (memcg && !mem_cgroup_is_root(memcg))
+	if (!mem_cgroup_is_root(memcg))
 		return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
 
 	if (unlikely(test_tsk_thread_flag(current, TIF_MEMDIE)))
@@ -629,9 +627,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 			.for_drop_caches = for_drop_caches,
 		};
 
-		if (!!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
-			continue;
-
 		if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
 			sc.nid = 0;
 
@@ -661,6 +656,7 @@ void drop_slab_node(int nid)
 		struct mem_cgroup *memcg = NULL;
 
 		freed = 0;
+		memcg = mem_cgroup_iter(NULL, NULL, NULL);
 		do {
 			freed += shrink_slab(GFP_KERNEL, nid, memcg, 0, true);
 		} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
@@ -2583,9 +2579,8 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
 
 		shrink_lruvec(lruvec, sc);
 
-		if (memcg)
-			shrink_slab(sc->gfp_mask, pgdat->node_id,
-				memcg, sc->priority, false);
+		shrink_slab(sc->gfp_mask, pgdat->node_id,
+			memcg, sc->priority, false);
 
 		/* Record the group's reclaim efficiency */
 		vmpressure(sc->gfp_mask, memcg, false,
@@ -2705,10 +2700,6 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 
 	shrink_node_memcgs(pgdat, sc);
 
-	if (!cgroup_reclaim(sc))
-		shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
-			sc->priority, false);
-
 	if (reclaim_state) {
 		sc->nr_reclaimed += reclaim_state->reclaimed_slab;
 		reclaim_state->reclaimed_slab = 0;