mm: move memcg hierarchy reclaim to generic reclaim code

Memory cgroup limit reclaim and traditional global pressure reclaim will
soon share the same code to reclaim from a hierarchical tree of memory
cgroups.

In preparation of this, move the two right next to each other in
shrink_zone().

The mem_cgroup_hierarchical_reclaim() polymath is split into a soft
limit reclaim function, which still does hierarchy walking on its own,
and a limit (shrinking) reclaim function, which relies on generic
reclaim code to walk the hierarchy.

Signed-off-by: Johannes Weiner <jweiner@redhat.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Ying Han <yinghan@google.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 85 insertions, 84 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bec451da7def..750ed1449955 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -370,8 +370,6 @@ enum charge_type {
 #define MEM_CGROUP_RECLAIM_NOSWAP       (1 << MEM_CGROUP_RECLAIM_NOSWAP_BIT)
 #define MEM_CGROUP_RECLAIM_SHRINK_BIT   0x1
 #define MEM_CGROUP_RECLAIM_SHRINK       (1 << MEM_CGROUP_RECLAIM_SHRINK_BIT)
-#define MEM_CGROUP_RECLAIM_SOFT_BIT     0x2
-#define MEM_CGROUP_RECLAIM_SOFT         (1 << MEM_CGROUP_RECLAIM_SOFT_BIT)
 
 static void mem_cgroup_get(struct mem_cgroup *memcg);
 static void mem_cgroup_put(struct mem_cgroup *memcg);
@@ -857,20 +855,33 @@ struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
         return memcg;
 }
 
-struct mem_cgroup_reclaim_cookie {
-        struct zone *zone;
-        int priority;
-        unsigned int generation;
-};
-
-static struct mem_cgroup *
-mem_cgroup_iter(struct mem_cgroup *root,
-                struct mem_cgroup *prev,
-                struct mem_cgroup_reclaim_cookie *reclaim)
+/**
+ * mem_cgroup_iter - iterate over memory cgroup hierarchy
+ * @root: hierarchy root
+ * @prev: previously returned memcg, NULL on first invocation
+ * @reclaim: cookie for shared reclaim walks, NULL for full walks
+ *
+ * Returns references to children of the hierarchy below @root, or
+ * @root itself, or %NULL after a full round-trip.
+ *
+ * Caller must pass the return value in @prev on subsequent
+ * invocations for reference counting, or use mem_cgroup_iter_break()
+ * to cancel a hierarchy walk before the round-trip is complete.
+ *
+ * Reclaimers can specify a zone and a priority level in @reclaim to
+ * divide up the memcgs in the hierarchy among all concurrent
+ * reclaimers operating on the same zone and priority.
+ */
+struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
+                                   struct mem_cgroup *prev,
+                                   struct mem_cgroup_reclaim_cookie *reclaim)
 {
         struct mem_cgroup *memcg = NULL;
         int id = 0;
 
+        if (mem_cgroup_disabled())
+                return NULL;
+
         if (!root)
                 root = root_mem_cgroup;
 
@@ -926,8 +937,13 @@ mem_cgroup_iter(struct mem_cgroup *root,
         return memcg;
 }
 
-static void mem_cgroup_iter_break(struct mem_cgroup *root,
-                                  struct mem_cgroup *prev)
+/**
+ * mem_cgroup_iter_break - abort a hierarchy walk prematurely
+ * @root: hierarchy root
+ * @prev: last visited hierarchy member as returned by mem_cgroup_iter()
+ */
+void mem_cgroup_iter_break(struct mem_cgroup *root,
+                           struct mem_cgroup *prev)
 {
         if (!root)
                 root = root_mem_cgroup;
@@ -1555,6 +1571,42 @@ u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
         return min(limit, memsw);
 }
 
+static unsigned long mem_cgroup_reclaim(struct mem_cgroup *memcg,
+                                        gfp_t gfp_mask,
+                                        unsigned long flags)
+{
+        unsigned long total = 0;
+        bool noswap = false;
+        int loop;
+
+        if (flags & MEM_CGROUP_RECLAIM_NOSWAP)
+                noswap = true;
+        if (!(flags & MEM_CGROUP_RECLAIM_SHRINK) && memcg->memsw_is_minimum)
+                noswap = true;
+
+        for (loop = 0; loop < MEM_CGROUP_MAX_RECLAIM_LOOPS; loop++) {
+                if (loop)
+                        drain_all_stock_async(memcg);
+                total += try_to_free_mem_cgroup_pages(memcg, gfp_mask, noswap);
+                /*
+                 * Allow limit shrinkers, which are triggered directly
+                 * by userspace, to catch signals and stop reclaim
+                 * after minimal progress, regardless of the margin.
+                 */
+                if (total && (flags & MEM_CGROUP_RECLAIM_SHRINK))
+                        break;
+                if (mem_cgroup_margin(memcg))
+                        break;
+                /*
+                 * If nothing was reclaimed after two attempts, there
+                 * may be no reclaimable pages in this hierarchy.
+                 */
+                if (loop && !total)
+                        break;
+        }
+        return total;
+}
+
 /**
  * test_mem_cgroup_node_reclaimable
  * @mem: the target memcg
@@ -1692,30 +1744,14 @@ bool mem_cgroup_reclaimable(struct mem_cgroup *memcg, bool noswap)
 }
 #endif
 
-/*
- * Scan the hierarchy if needed to reclaim memory. We remember the last child
- * we reclaimed from, so that we don't end up penalizing one child extensively
- * based on its position in the children list.
- *
- * root_memcg is the original ancestor that we've been reclaim from.
- *
- * We give up and return to the caller when we visit root_memcg twice.
- * (other groups can be removed while we're walking....)
- *
- * If shrink==true, for avoiding to free too much, this returns immedieately.
- */
-static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_memcg,
-                                                struct zone *zone,
-                                                gfp_t gfp_mask,
-                                                unsigned long reclaim_options,
-                                                unsigned long *total_scanned)
+static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg,
+                                   struct zone *zone,
+                                   gfp_t gfp_mask,
+                                   unsigned long *total_scanned)
 {
         struct mem_cgroup *victim = NULL;
-        int ret, total = 0;
+        int total = 0;
         int loop = 0;
-        bool noswap = reclaim_options & MEM_CGROUP_RECLAIM_NOSWAP;
-        bool shrink = reclaim_options & MEM_CGROUP_RECLAIM_SHRINK;
-        bool check_soft = reclaim_options & MEM_CGROUP_RECLAIM_SOFT;
         unsigned long excess;
         unsigned long nr_scanned;
         struct mem_cgroup_reclaim_cookie reclaim = {
@@ -1725,29 +1761,17 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_memcg,
 
         excess = res_counter_soft_limit_excess(&root_memcg->res) >> PAGE_SHIFT;
 
-        /* If memsw_is_minimum==1, swap-out is of-no-use. */
-        if (!check_soft && !shrink && root_memcg->memsw_is_minimum)
-                noswap = true;
-
         while (1) {
                 victim = mem_cgroup_iter(root_memcg, victim, &reclaim);
                 if (!victim) {
                         loop++;
-                        /*
-                         * We are not draining per cpu cached charges during
-                         * soft limit reclaim  because global reclaim doesn't
-                         * care about charges. It tries to free some memory and
-                         * charges will not give any.
-                         */
-                        if (!check_soft && loop >= 1)
-                                drain_all_stock_async(root_memcg);
                         if (loop >= 2) {
                                 /*
                                  * If we have not been able to reclaim
                                  * anything, it might because there are
                                  * no reclaimable pages under this hierarchy
                                  */
-                                if (!check_soft || !total)
+                                if (!total)
                                         break;
                                 /*
                                  * We want to do more targeted reclaim.
@@ -1761,30 +1785,12 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_memcg,
                         }
                         continue;
                 }
-                if (!mem_cgroup_reclaimable(victim, noswap)) {
-                        /* this cgroup's local usage == 0 */
+                if (!mem_cgroup_reclaimable(victim, false))
                         continue;
-                }
-                /* we use swappiness of local cgroup */
-                if (check_soft) {
-                        ret = mem_cgroup_shrink_node_zone(victim, gfp_mask,
-                                noswap, zone, &nr_scanned);
-                        *total_scanned += nr_scanned;
-                } else
-                        ret = try_to_free_mem_cgroup_pages(victim, gfp_mask,
-                                                noswap);
-                total += ret;
-                /*
-                 * At shrinking usage, we can't check we should stop here or
-                 * reclaim more. It's depends on callers. last_scanned_child
-                 * will work enough for keeping fairness under tree.
-                 */
-                if (shrink)
-                        break;
-                if (check_soft) {
-                        if (!res_counter_soft_limit_excess(&root_memcg->res))
-                                break;
-                } else if (mem_cgroup_margin(root_memcg))
+                total += mem_cgroup_shrink_node_zone(victim, gfp_mask, false,
+                                                     zone, &nr_scanned);
+                *total_scanned += nr_scanned;
+                if (!res_counter_soft_limit_excess(&root_memcg->res))
                         break;
         }
         mem_cgroup_iter_break(root_memcg, victim);
@@ -2281,8 +2287,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
         if (!(gfp_mask & __GFP_WAIT))
                 return CHARGE_WOULDBLOCK;
 
-        ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
-                                              gfp_mask, flags, NULL);
+        ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags);
         if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
                 return CHARGE_RETRY;
         /*
@@ -3559,9 +3564,8 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
                 if (!ret)
                         break;
 
-                mem_cgroup_hierarchical_reclaim(memcg, NULL, GFP_KERNEL,
-                                                MEM_CGROUP_RECLAIM_SHRINK,
-                                                NULL);
+                mem_cgroup_reclaim(memcg, GFP_KERNEL,
+                                   MEM_CGROUP_RECLAIM_SHRINK);
                 curusage = res_counter_read_u64(&memcg->res, RES_USAGE);
                 /* Usage is reduced ? */
                 if (curusage >= oldusage)
@@ -3619,10 +3623,9 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
                 if (!ret)
                         break;
 
-                mem_cgroup_hierarchical_reclaim(memcg, NULL, GFP_KERNEL,
-                                                MEM_CGROUP_RECLAIM_NOSWAP |
-                                                MEM_CGROUP_RECLAIM_SHRINK,
-                                                NULL);
+                mem_cgroup_reclaim(memcg, GFP_KERNEL,
+                                   MEM_CGROUP_RECLAIM_NOSWAP |
+                                   MEM_CGROUP_RECLAIM_SHRINK);
                 curusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
                 /* Usage is reduced ? */
                 if (curusage >= oldusage)
@@ -3665,10 +3668,8 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
                         break;
 
                 nr_scanned = 0;
-                reclaimed = mem_cgroup_hierarchical_reclaim(mz->mem, zone,
-                                                gfp_mask,
-                                                MEM_CGROUP_RECLAIM_SOFT,
-                                                &nr_scanned);
+                reclaimed = mem_cgroup_soft_reclaim(mz->mem, zone,
+                                                    gfp_mask, &nr_scanned);
                 nr_reclaimed += reclaimed;
                 *total_scanned += nr_scanned;
                 spin_lock(&mctz->lock);