revert "memcg, vmscan: integrate soft reclaim tighter with zone shrinking code"

Revert commit 3b38722efd9f ("memcg, vmscan: integrate soft reclaim
tighter with zone shrinking code")

I merged this prematurely - Michal and Johannes still disagree about the
overall design direction and the future remains unclear.

Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 168 insertions, 57 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 852dbec07ce6..1c52ddbc839b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1991,28 +1991,57 @@ static bool mem_cgroup_reclaimable(struct mem_cgroup *memcg, bool noswap)
 }
 #endif
 
-/*
- * A group is eligible for the soft limit reclaim if
- *      a) it is over its soft limit
- *      b) any parent up the hierarchy is over its soft limit
- */
-bool mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg)
-{
-        struct mem_cgroup *parent = memcg;
-
-        if (res_counter_soft_limit_excess(&memcg->res))
-                return true;
-
-        /*
-         * If any parent up the hierarchy is over its soft limit then we
-         * have to obey and reclaim from this group as well.
-         */
-        while ((parent = parent_mem_cgroup(parent))) {
-                if (res_counter_soft_limit_excess(&parent->res))
-                        return true;
+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 total = 0;
+        int loop = 0;
+        unsigned long excess;
+        unsigned long nr_scanned;
+        struct mem_cgroup_reclaim_cookie reclaim = {
+                .zone = zone,
+                .priority = 0,
+        };
+
+        excess = res_counter_soft_limit_excess(&root_memcg->res) >> PAGE_SHIFT;
+
+        while (1) {
+                victim = mem_cgroup_iter(root_memcg, victim, &reclaim);
+                if (!victim) {
+                        loop++;
+                        if (loop >= 2) {
+                                /*
+                                 * If we have not been able to reclaim
+                                 * anything, it might because there are
+                                 * no reclaimable pages under this hierarchy
+                                 */
+                                if (!total)
+                                        break;
+                                /*
+                                 * We want to do more targeted reclaim.
+                                 * excess >> 2 is not to excessive so as to
+                                 * reclaim too much, nor too less that we keep
+                                 * coming back to reclaim from this cgroup
+                                 */
+                                if (total >= (excess >> 2) ||
+                                        (loop > MEM_CGROUP_MAX_RECLAIM_LOOPS))
+                                        break;
+                        }
+                        continue;
+                }
+                if (!mem_cgroup_reclaimable(victim, false))
+                        continue;
+                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;
         }
-
-        return false;
+        mem_cgroup_iter_break(root_memcg, victim);
+        return total;
 }
 
 static DEFINE_SPINLOCK(memcg_oom_lock);
@@ -4761,6 +4790,98 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
         return ret;
 }
 
+unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
+                                            gfp_t gfp_mask,
+                                            unsigned long *total_scanned)
+{
+        unsigned long nr_reclaimed = 0;
+        struct mem_cgroup_per_zone *mz, *next_mz = NULL;
+        unsigned long reclaimed;
+        int loop = 0;
+        struct mem_cgroup_tree_per_zone *mctz;
+        unsigned long long excess;
+        unsigned long nr_scanned;
+
+        if (order > 0)
+                return 0;
+
+        mctz = soft_limit_tree_node_zone(zone_to_nid(zone), zone_idx(zone));
+        /*
+         * This loop can run a while, specially if mem_cgroup's continuously
+         * keep exceeding their soft limit and putting the system under
+         * pressure
+         */
+        do {
+                if (next_mz)
+                        mz = next_mz;
+                else
+                        mz = mem_cgroup_largest_soft_limit_node(mctz);
+                if (!mz)
+                        break;
+
+                nr_scanned = 0;
+                reclaimed = mem_cgroup_soft_reclaim(mz->memcg, zone,
+                                                    gfp_mask, &nr_scanned);
+                nr_reclaimed += reclaimed;
+                *total_scanned += nr_scanned;
+                spin_lock(&mctz->lock);
+
+                /*
+                 * If we failed to reclaim anything from this memory cgroup
+                 * it is time to move on to the next cgroup
+                 */
+                next_mz = NULL;
+                if (!reclaimed) {
+                        do {
+                                /*
+                                 * Loop until we find yet another one.
+                                 *
+                                 * By the time we get the soft_limit lock
+                                 * again, someone might have aded the
+                                 * group back on the RB tree. Iterate to
+                                 * make sure we get a different mem.
+                                 * mem_cgroup_largest_soft_limit_node returns
+                                 * NULL if no other cgroup is present on
+                                 * the tree
+                                 */
+                                next_mz =
+                                __mem_cgroup_largest_soft_limit_node(mctz);
+                                if (next_mz == mz)
+                                        css_put(&next_mz->memcg->css);
+                                else /* next_mz == NULL or other memcg */
+                                        break;
+                        } while (1);
+                }
+                __mem_cgroup_remove_exceeded(mz->memcg, mz, mctz);
+                excess = res_counter_soft_limit_excess(&mz->memcg->res);
+                /*
+                 * One school of thought says that we should not add
+                 * back the node to the tree if reclaim returns 0.
+                 * But our reclaim could return 0, simply because due
+                 * to priority we are exposing a smaller subset of
+                 * memory to reclaim from. Consider this as a longer
+                 * term TODO.
+                 */
+                /* If excess == 0, no tree ops */
+                __mem_cgroup_insert_exceeded(mz->memcg, mz, mctz, excess);
+                spin_unlock(&mctz->lock);
+                css_put(&mz->memcg->css);
+                loop++;
+                /*
+                 * Could not reclaim anything and there are no more
+                 * mem cgroups to try or we seem to be looping without
+                 * reclaiming anything.
+                 */
+                if (!nr_reclaimed &&
+                        (next_mz == NULL ||
+                        loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
+                        break;
+        } while (!nr_reclaimed);
+        if (next_mz)
+                css_put(&next_mz->memcg->css);
+        return nr_reclaimed;
+}
+
 /**
  * mem_cgroup_force_empty_list - clears LRU of a group
  * @memcg: group to clear
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0e081cada4ba..beb35778c69f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -139,21 +139,11 @@ static bool global_reclaim(struct scan_control *sc)
 {
         return !sc->target_mem_cgroup;
 }
-
-static bool mem_cgroup_should_soft_reclaim(struct scan_control *sc)
-{
-        return !mem_cgroup_disabled() && global_reclaim(sc);
-}
 #else
 static bool global_reclaim(struct scan_control *sc)
 {
         return true;
 }
-
-static bool mem_cgroup_should_soft_reclaim(struct scan_control *sc)
-{
-        return false;
-}
 #endif
 
 unsigned long zone_reclaimable_pages(struct zone *zone)
@@ -2174,8 +2164,7 @@ static inline bool should_continue_reclaim(struct zone *zone,
         }
 }
 
-static void
-__shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
+static void shrink_zone(struct zone *zone, struct scan_control *sc)
 {
         unsigned long nr_reclaimed, nr_scanned;
 
@@ -2194,12 +2183,6 @@ __shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
                 do {
                         struct lruvec *lruvec;
 
-                        if (soft_reclaim &&
-                            !mem_cgroup_soft_reclaim_eligible(memcg)) {
-                                memcg = mem_cgroup_iter(root, memcg, &reclaim);
-                                continue;
-                        }
-
                         lruvec = mem_cgroup_zone_lruvec(zone, memcg);
 
                         shrink_lruvec(lruvec, sc);
@@ -2230,24 +2213,6 @@ __shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
                                          sc->nr_scanned - nr_scanned, sc));
 }
 
-
-static void shrink_zone(struct zone *zone, struct scan_control *sc)
-{
-        bool do_soft_reclaim = mem_cgroup_should_soft_reclaim(sc);
-        unsigned long nr_scanned = sc->nr_scanned;
-
-        __shrink_zone(zone, sc, do_soft_reclaim);
-
-        /*
-         * No group is over the soft limit or those that are do not have
-         * pages in the zone we are reclaiming so we have to reclaim everybody
-         */
-        if (do_soft_reclaim && (sc->nr_scanned == nr_scanned)) {
-                __shrink_zone(zone, sc, false);
-                return;
-        }
-}
-
 /* Returns true if compaction should go ahead for a high-order request */
 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
 {
@@ -2309,6 +2274,8 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 {
         struct zoneref *z;
         struct zone *zone;
+        unsigned long nr_soft_reclaimed;
+        unsigned long nr_soft_scanned;
         bool aborted_reclaim = false;
 
         /*
@@ -2348,6 +2315,18 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
                                         continue;
                                 }
                         }
+                        /*
+                         * This steals pages from memory cgroups over softlimit
+                         * and returns the number of reclaimed pages and
+                         * scanned pages. This works for global memory pressure
+                         * and balancing, not for a memcg's limit.
+                         */
+                        nr_soft_scanned = 0;
+                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
+                                                sc->order, sc->gfp_mask,
+                                                &nr_soft_scanned);
+                        sc->nr_reclaimed += nr_soft_reclaimed;
+                        sc->nr_scanned += nr_soft_scanned;
                         /* need some check for avoid more shrink_zone() */
                 }
 
@@ -2941,6 +2920,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 {
         int i;
         int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
+        unsigned long nr_soft_reclaimed;
+        unsigned long nr_soft_scanned;
         struct scan_control sc = {
                 .gfp_mask = GFP_KERNEL,
                 .priority = DEF_PRIORITY,
@@ -3055,6 +3036,15 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 
                         sc.nr_scanned = 0;
 
+                        nr_soft_scanned = 0;
+                        /*
+                         * Call soft limit reclaim before calling shrink_zone.
+                         */
+                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
+                                                        order, sc.gfp_mask,
+                                                        &nr_soft_scanned);
+                        sc.nr_reclaimed += nr_soft_reclaimed;
+
                         /*
                          * There should be no need to raise the scanning
                          * priority if enough pages are already being scanned