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>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 5e9840f509804df5e49224a12bbbd079177ee4f6..0629121f2c0b56f3f103d14cec434815f2780ad0 100644 (file)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -144,7 +144,8 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
 }
 
 unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
-                                               gfp_t gfp_mask);
+                                               gfp_t gfp_mask,
+                                               unsigned long *total_scanned);
 u64 mem_cgroup_get_limit(struct mem_cgroup *mem);
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
@@ -338,7 +339,8 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
 
 static inline
 unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
-                                           gfp_t gfp_mask)
+                                           gfp_t gfp_mask,
+                                           unsigned long *total_scanned)
 {
        return 0;
 }

diff --git a/include/linux/swap.h b/include/linux/swap.h
index a5c6da5d8df8dd5ad28b6b9525bfa787caa3e74d..384eb5fe530b8e90c44c9f65ebb719f965cf65df 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -257,7 +257,8 @@ extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem,
 extern 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);
 extern int __isolate_lru_page(struct page *page, int mode, int file);
 extern unsigned long shrink_all_memory(unsigned long nr_pages);
 extern int vm_swappiness;

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fc259926c1709754336b22bcb762ef905b65ec1e..e41a6c26f1e7020c2bab73dc31295a1a855e0313 100644 (file)
--- 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 7e0116150dc73a02b762cb8939c5db34688aa194..9ce6ec84328eb2f3e7a29cf1f1d205570019f136 100644 (file)
--- 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