memcg: count the soft_limit reclaim in global background reclaim

The global kswapd scans per-zone LRU and reclaims pages regardless of the
cgroup. It breaks memory isolation since one cgroup can end up reclaiming
pages from another cgroup. Instead we should rely on memcg-aware target
reclaim including per-memcg kswapd and soft_limit hierarchical reclaim under
memory pressure.

In the global background reclaim, we do soft reclaim before scanning the
per-zone LRU. However, the return value is ignored. This patch is the first
step to skip shrink_zone() if soft_limit reclaim does enough work.

This is part of the effort which tries to reduce reclaiming pages in global
LRU in memcg. The per-memcg background reclaim patchset further enhances the
per-cgroup targetting reclaim, which I should have V4 posted shortly.

Try running multiple memory intensive workloads within seperate memcgs. Watch
the counters of soft_steal in memory.stat.

  $ cat /dev/cgroup/A/memory.stat | grep 'soft'
  soft_steal 240000
  soft_scan 240000
  total_soft_steal 240000
  total_soft_scan 240000

This patch:

In the global background reclaim, we do soft reclaim before scanning the
per-zone LRU.  However, the return value is ignored.

We would like to skip shrink_zone() if soft_limit reclaim does enough
work.  Also, we need to make the memory pressure balanced across per-memcg
zones, like the logic vm-core.  This patch is the first step where we
start with counting the nr_scanned and nr_reclaimed from soft_limit
reclaim into the global scan_control.

Signed-off-by: Ying Han <yinghan@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Acked-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 33 insertions, 12 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fc259926c170..e41a6c26f1e7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1433,7 +1433,8 @@ mem_cgroup_select_victim(struct mem_cgroup *root_mem)
 static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
                                                 struct zone *zone,
                                                 gfp_t gfp_mask,
-                                                unsigned long reclaim_options)
+                                                unsigned long reclaim_options,
+                                                unsigned long *total_scanned)
 {
         struct mem_cgroup *victim;
         int ret, total = 0;
@@ -1442,6 +1443,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
         bool shrink = reclaim_options & MEM_CGROUP_RECLAIM_SHRINK;
         bool check_soft = reclaim_options & MEM_CGROUP_RECLAIM_SOFT;
         unsigned long excess;
+        unsigned long nr_scanned;
 
         excess = res_counter_soft_limit_excess(&root_mem->res) >> PAGE_SHIFT;
 
@@ -1484,10 +1486,12 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
                         continue;
                 }
                 /* we use swappiness of local cgroup */
-                if (check_soft)
+                if (check_soft) {
                         ret = mem_cgroup_shrink_node_zone(victim, gfp_mask,
-                                noswap, get_swappiness(victim), zone);
-                else
+                                noswap, get_swappiness(victim), zone,
+                                &nr_scanned);
+                        *total_scanned += nr_scanned;
+                } else
                         ret = try_to_free_mem_cgroup_pages(victim, gfp_mask,
                                                 noswap, get_swappiness(victim));
                 css_put(&victim->css);
@@ -1928,7 +1932,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
                 return CHARGE_WOULDBLOCK;
 
         ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
-                                              gfp_mask, flags);
+                                              gfp_mask, flags, NULL);
         if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
                 return CHARGE_RETRY;
         /*
@@ -3211,7 +3215,8 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
                         break;
 
                 mem_cgroup_hierarchical_reclaim(memcg, NULL, GFP_KERNEL,
-                                                MEM_CGROUP_RECLAIM_SHRINK);
+                                                MEM_CGROUP_RECLAIM_SHRINK,
+                                                NULL);
                 curusage = res_counter_read_u64(&memcg->res, RES_USAGE);
                 /* Usage is reduced ? */
                 if (curusage >= oldusage)
@@ -3271,7 +3276,8 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
 
                 mem_cgroup_hierarchical_reclaim(memcg, NULL, GFP_KERNEL,
                                                 MEM_CGROUP_RECLAIM_NOSWAP |
-                                                MEM_CGROUP_RECLAIM_SHRINK);
+                                                MEM_CGROUP_RECLAIM_SHRINK,
+                                                NULL);
                 curusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
                 /* Usage is reduced ? */
                 if (curusage >= oldusage)
@@ -3285,7 +3291,8 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
 }
 
 unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
-                                            gfp_t gfp_mask)
+                                            gfp_t gfp_mask,
+                                            unsigned long *total_scanned)
 {
         unsigned long nr_reclaimed = 0;
         struct mem_cgroup_per_zone *mz, *next_mz = NULL;
@@ -3293,6 +3300,7 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
         int loop = 0;
         struct mem_cgroup_tree_per_zone *mctz;
         unsigned long long excess;
+        unsigned long nr_scanned;
 
         if (order > 0)
                 return 0;
@@ -3311,10 +3319,13 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
                 if (!mz)
                         break;
 
+                nr_scanned = 0;
                 reclaimed = mem_cgroup_hierarchical_reclaim(mz->mem, zone,
                                                 gfp_mask,
-                                                MEM_CGROUP_RECLAIM_SOFT);
+                                                MEM_CGROUP_RECLAIM_SOFT,
+                                                &nr_scanned);
                 nr_reclaimed += reclaimed;
+                *total_scanned += nr_scanned;
                 spin_lock(&mctz->lock);
 
                 /*
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7e0116150dc7..9ce6ec84328e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2171,9 +2171,11 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
                                                 gfp_t gfp_mask, bool noswap,
                                                 unsigned int swappiness,
-                                                struct zone *zone)
+                                                struct zone *zone,
+                                                unsigned long *nr_scanned)
 {
         struct scan_control sc = {
+                .nr_scanned = 0,
                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
                 .may_writepage = !laptop_mode,
                 .may_unmap = 1,
@@ -2182,6 +2184,7 @@ unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
                 .order = 0,
                 .mem_cgroup = mem,
         };
+
         sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
                         (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
 
@@ -2200,6 +2203,7 @@ unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
 
         trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
 
+        *nr_scanned = sc.nr_scanned;
         return sc.nr_reclaimed;
 }
 
@@ -2347,6 +2351,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
         int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
         unsigned long total_scanned;
         struct reclaim_state *reclaim_state = current->reclaim_state;
+        unsigned long nr_soft_reclaimed;
+        unsigned long nr_soft_scanned;
         struct scan_control sc = {
                 .gfp_mask = GFP_KERNEL,
                 .may_unmap = 1,
@@ -2439,11 +2445,15 @@ loop_again:
 
                         sc.nr_scanned = 0;
 
+                        nr_soft_scanned = 0;
                         /*
                          * Call soft limit reclaim before calling shrink_zone.
-                         * For now we ignore the return value
                          */
-                        mem_cgroup_soft_limit_reclaim(zone, order, sc.gfp_mask);
+                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
+                                                        order, sc.gfp_mask,
+                                                        &nr_soft_scanned);
+                        sc.nr_reclaimed += nr_soft_reclaimed;
+                        total_scanned += nr_soft_scanned;
 
                         /*
                          * We put equal pressure on every zone, unless