lib: objagg: implement optimization hints assembly and use hints for object creation

Implement simple greedy algo to find more optimized root-delta tree for
a given objagg instance. This "hints" can be used by a driver to:
1) check if the hints are better (driver's choice) than the original
   objagg tree. Driver does comparison of objagg stats and hints stats.
2) use the hints to create a new objagg instance which will construct
   the root-delta tree according to the passed hints. Currently, only a
   simple greedy algorithm is implemented. Basically it finds the roots
   according to the maximal possible user count including deltas.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 802 insertions, 22 deletions

diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_erp.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_erp.c
index 2941967e1cc5..302070a74f2e 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_erp.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_erp.c
@@ -1200,6 +1200,32 @@ mlxsw_sp_acl_erp_delta_fill(const struct mlxsw_sp_acl_erp_key *parent_key,
         return 0;
 }
 
+static bool mlxsw_sp_acl_erp_delta_check(void *priv, const void *parent_obj,
+                                         const void *obj)
+{
+        const struct mlxsw_sp_acl_erp_key *parent_key = parent_obj;
+        const struct mlxsw_sp_acl_erp_key *key = obj;
+        u16 delta_start;
+        u8 delta_mask;
+        int err;
+
+        err = mlxsw_sp_acl_erp_delta_fill(parent_key, key,
+                                          &delta_start, &delta_mask);
+        return err ? false : true;
+}
+
+static int mlxsw_sp_acl_erp_hints_obj_cmp(const void *obj1, const void *obj2)
+{
+        const struct mlxsw_sp_acl_erp_key *key1 = obj1;
+        const struct mlxsw_sp_acl_erp_key *key2 = obj2;
+
+        /* For hints purposes, two objects are considered equal
+         * in case the masks are the same. Does not matter what
+         * the "ctcam" value is.
+         */
+        return memcmp(key1->mask, key2->mask, sizeof(key1->mask));
+}
+
 static void *mlxsw_sp_acl_erp_delta_create(void *priv, void *parent_obj,
                                            void *obj)
 {
@@ -1254,12 +1280,17 @@ static void mlxsw_sp_acl_erp_delta_destroy(void *priv, void *delta_priv)
         kfree(delta);
 }
 
-static void *mlxsw_sp_acl_erp_root_create(void *priv, void *obj)
+static void *mlxsw_sp_acl_erp_root_create(void *priv, void *obj,
+                                          unsigned int root_id)
 {
         struct mlxsw_sp_acl_atcam_region *aregion = priv;
         struct mlxsw_sp_acl_erp_table *erp_table = aregion->erp_table;
         struct mlxsw_sp_acl_erp_key *key = obj;
 
+        if (!key->ctcam &&
+            root_id != OBJAGG_OBJ_ROOT_ID_INVALID &&
+            root_id >= MLXSW_SP_ACL_ERP_MAX_PER_REGION)
+                return ERR_PTR(-ENOBUFS);
         return erp_table->ops->erp_create(erp_table, key);
 }
 
@@ -1273,6 +1304,8 @@ static void mlxsw_sp_acl_erp_root_destroy(void *priv, void *root_priv)
 
 static const struct objagg_ops mlxsw_sp_acl_erp_objagg_ops = {
         .obj_size = sizeof(struct mlxsw_sp_acl_erp_key),
+        .delta_check = mlxsw_sp_acl_erp_delta_check,
+        .hints_obj_cmp = mlxsw_sp_acl_erp_hints_obj_cmp,
         .delta_create = mlxsw_sp_acl_erp_delta_create,
         .delta_destroy = mlxsw_sp_acl_erp_delta_destroy,
         .root_create = mlxsw_sp_acl_erp_root_create,
@@ -1290,7 +1323,7 @@ mlxsw_sp_acl_erp_table_create(struct mlxsw_sp_acl_atcam_region *aregion)
                 return ERR_PTR(-ENOMEM);
 
         erp_table->objagg = objagg_create(&mlxsw_sp_acl_erp_objagg_ops,
-                                          aregion);
+                                          NULL, aregion);
         if (IS_ERR(erp_table->objagg)) {
                 err = PTR_ERR(erp_table->objagg);
                 goto err_objagg_create;
diff --git a/include/linux/objagg.h b/include/linux/objagg.h
index 34f38c186ea0..a675286df1af 100644
--- a/include/linux/objagg.h
+++ b/include/linux/objagg.h
@@ -6,14 +6,19 @@
 
 struct objagg_ops {
         size_t obj_size;
+        bool (*delta_check)(void *priv, const void *parent_obj,
+                            const void *obj);
+        int (*hints_obj_cmp)(const void *obj1, const void *obj2);
         void * (*delta_create)(void *priv, void *parent_obj, void *obj);
         void (*delta_destroy)(void *priv, void *delta_priv);
-        void * (*root_create)(void *priv, void *obj);
+        void * (*root_create)(void *priv, void *obj, unsigned int root_id);
+#define OBJAGG_OBJ_ROOT_ID_INVALID UINT_MAX
         void (*root_destroy)(void *priv, void *root_priv);
 };
 
 struct objagg;
 struct objagg_obj;
+struct objagg_hints;
 
 const void *objagg_obj_root_priv(const struct objagg_obj *objagg_obj);
 const void *objagg_obj_delta_priv(const struct objagg_obj *objagg_obj);
@@ -21,7 +26,8 @@ const void *objagg_obj_raw(const struct objagg_obj *objagg_obj);
 
 struct objagg_obj *objagg_obj_get(struct objagg *objagg, void *obj);
 void objagg_obj_put(struct objagg *objagg, struct objagg_obj *objagg_obj);
-struct objagg *objagg_create(const struct objagg_ops *ops, void *priv);
+struct objagg *objagg_create(const struct objagg_ops *ops,
+                             struct objagg_hints *hints, void *priv);
 void objagg_destroy(struct objagg *objagg);
 
 struct objagg_obj_stats {
@@ -43,4 +49,14 @@ struct objagg_stats {
 const struct objagg_stats *objagg_stats_get(struct objagg *objagg);
 void objagg_stats_put(const struct objagg_stats *objagg_stats);
 
+enum objagg_opt_algo_type {
+        OBJAGG_OPT_ALGO_SIMPLE_GREEDY,
+};
+
+struct objagg_hints *objagg_hints_get(struct objagg *objagg,
+                                      enum objagg_opt_algo_type opt_algo_type);
+void objagg_hints_put(struct objagg_hints *objagg_hints);
+const struct objagg_stats *
+objagg_hints_stats_get(struct objagg_hints *objagg_hints);
+
 #endif
diff --git a/lib/objagg.c b/lib/objagg.c
index dae390bcef1a..befe8a47d080 100644
--- a/lib/objagg.c
+++ b/lib/objagg.c
@@ -4,6 +4,7 @@
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/rhashtable.h>
+#include <linux/idr.h>
 #include <linux/list.h>
 #include <linux/sort.h>
 #include <linux/objagg.h>
@@ -11,6 +12,34 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/objagg.h>
 
+struct objagg_hints {
+        struct rhashtable node_ht;
+        struct rhashtable_params ht_params;
+        struct list_head node_list;
+        unsigned int node_count;
+        unsigned int root_count;
+        unsigned int refcount;
+        const struct objagg_ops *ops;
+};
+
+struct objagg_hints_node {
+        struct rhash_head ht_node; /* member of objagg_hints->node_ht */
+        struct list_head list; /* member of objagg_hints->node_list */
+        struct objagg_hints_node *parent;
+        unsigned int root_id;
+        struct objagg_obj_stats_info stats_info;
+        unsigned long obj[0];
+};
+
+static struct objagg_hints_node *
+objagg_hints_lookup(struct objagg_hints *objagg_hints, void *obj)
+{
+        if (!objagg_hints)
+                return NULL;
+        return rhashtable_lookup_fast(&objagg_hints->node_ht, obj,
+                                      objagg_hints->ht_params);
+}
+
 struct objagg {
         const struct objagg_ops *ops;
         void *priv;
@@ -18,6 +47,8 @@ struct objagg {
         struct rhashtable_params ht_params;
         struct list_head obj_list;
         unsigned int obj_count;
+        struct ida root_ida;
+        struct objagg_hints *hints;
 };
 
 struct objagg_obj {
@@ -30,6 +61,7 @@ struct objagg_obj {
                 void *delta_priv; /* user delta private */
                 void *root_priv; /* user root private */
         };
+        unsigned int root_id;
         unsigned int refcount; /* counts number of users of this object
                                 * including nested objects
                                 */
@@ -130,7 +162,8 @@ static struct objagg_obj *objagg_obj_lookup(struct objagg *objagg, void *obj)
 
 static int objagg_obj_parent_assign(struct objagg *objagg,
                                     struct objagg_obj *objagg_obj,
-                                    struct objagg_obj *parent)
+                                    struct objagg_obj *parent,
+                                    bool take_parent_ref)
 {
         void *delta_priv;
 
@@ -144,7 +177,8 @@ static int objagg_obj_parent_assign(struct objagg *objagg,
          */
         objagg_obj->parent = parent;
         objagg_obj->delta_priv = delta_priv;
-        objagg_obj_ref_inc(objagg_obj->parent);
+        if (take_parent_ref)
+                objagg_obj_ref_inc(objagg_obj->parent);
         trace_objagg_obj_parent_assign(objagg, objagg_obj,
                                        parent,
                                        parent->refcount);
@@ -164,7 +198,7 @@ static int objagg_obj_parent_lookup_assign(struct objagg *objagg,
                 if (!objagg_obj_is_root(objagg_obj_cur))
                         continue;
                 err = objagg_obj_parent_assign(objagg, objagg_obj,
-                                               objagg_obj_cur);
+                                               objagg_obj_cur, true);
                 if (!err)
                         return 0;
         }
@@ -184,16 +218,68 @@ static void objagg_obj_parent_unassign(struct objagg *objagg,
         __objagg_obj_put(objagg, objagg_obj->parent);
 }
 
+static int objagg_obj_root_id_alloc(struct objagg *objagg,
+                                    struct objagg_obj *objagg_obj,
+                                    struct objagg_hints_node *hnode)
+{
+        unsigned int min, max;
+        int root_id;
+
+        /* In case there are no hints available, the root id is invalid. */
+        if (!objagg->hints) {
+                objagg_obj->root_id = OBJAGG_OBJ_ROOT_ID_INVALID;
+                return 0;
+        }
+
+        if (hnode) {
+                min = hnode->root_id;
+                max = hnode->root_id;
+        } else {
+                /* For objects with no hint, start after the last
+                 * hinted root_id.
+                 */
+                min = objagg->hints->root_count;
+                max = ~0;
+        }
+
+        root_id = ida_alloc_range(&objagg->root_ida, min, max, GFP_KERNEL);
+
+        if (root_id < 0)
+                return root_id;
+        objagg_obj->root_id = root_id;
+        return 0;
+}
+
+static void objagg_obj_root_id_free(struct objagg *objagg,
+                                    struct objagg_obj *objagg_obj)
+{
+        if (!objagg->hints)
+                return;
+        ida_free(&objagg->root_ida, objagg_obj->root_id);
+}
+
 static int objagg_obj_root_create(struct objagg *objagg,
-                                  struct objagg_obj *objagg_obj)
+                                  struct objagg_obj *objagg_obj,
+                                  struct objagg_hints_node *hnode)
 {
-        objagg_obj->root_priv = objagg->ops->root_create(objagg->priv,
-                                                         objagg_obj->obj);
-        if (IS_ERR(objagg_obj->root_priv))
-                return PTR_ERR(objagg_obj->root_priv);
+        int err;
 
+        err = objagg_obj_root_id_alloc(objagg, objagg_obj, hnode);
+        if (err)
+                return err;
+        objagg_obj->root_priv = objagg->ops->root_create(objagg->priv,
+                                                         objagg_obj->obj,
+                                                         objagg_obj->root_id);
+        if (IS_ERR(objagg_obj->root_priv)) {
+                err = PTR_ERR(objagg_obj->root_priv);
+                goto err_root_create;
+        }
         trace_objagg_obj_root_create(objagg, objagg_obj);
         return 0;
+
+err_root_create:
+        objagg_obj_root_id_free(objagg, objagg_obj);
+        return err;
 }
 
 static void objagg_obj_root_destroy(struct objagg *objagg,
@@ -201,19 +287,69 @@ static void objagg_obj_root_destroy(struct objagg *objagg,
 {
         trace_objagg_obj_root_destroy(objagg, objagg_obj);
         objagg->ops->root_destroy(objagg->priv, objagg_obj->root_priv);
+        objagg_obj_root_id_free(objagg, objagg_obj);
+}
+
+static struct objagg_obj *__objagg_obj_get(struct objagg *objagg, void *obj);
+
+static int objagg_obj_init_with_hints(struct objagg *objagg,
+                                      struct objagg_obj *objagg_obj,
+                                      bool *hint_found)
+{
+        struct objagg_hints_node *hnode;
+        struct objagg_obj *parent;
+        int err;
+
+        hnode = objagg_hints_lookup(objagg->hints, objagg_obj->obj);
+        if (!hnode) {
+                *hint_found = false;
+                return 0;
+        }
+        *hint_found = true;
+
+        if (!hnode->parent)
+                return objagg_obj_root_create(objagg, objagg_obj, hnode);
+
+        parent = __objagg_obj_get(objagg, hnode->parent->obj);
+        if (IS_ERR(parent))
+                return PTR_ERR(parent);
+
+        err = objagg_obj_parent_assign(objagg, objagg_obj, parent, false);
+        if (err) {
+                *hint_found = false;
+                err = 0;
+                goto err_parent_assign;
+        }
+
+        return 0;
+
+err_parent_assign:
+        objagg_obj_put(objagg, parent);
+        return err;
 }
 
 static int objagg_obj_init(struct objagg *objagg,
                            struct objagg_obj *objagg_obj)
 {
+        bool hint_found;
         int err;
 
+        /* First, try to use hints if they are available and
+         * if they provide result.
+         */
+        err = objagg_obj_init_with_hints(objagg, objagg_obj, &hint_found);
+        if (err)
+                return err;
+
+        if (hint_found)
+                return 0;
+
         /* Try to find if the object can be aggregated under an existing one. */
         err = objagg_obj_parent_lookup_assign(objagg, objagg_obj);
         if (!err)
                 return 0;
         /* If aggregation is not possible, make the object a root. */
-        return objagg_obj_root_create(objagg, objagg_obj);
+        return objagg_obj_root_create(objagg, objagg_obj, NULL);
 }
 
 static void objagg_obj_fini(struct objagg *objagg,
@@ -349,8 +485,9 @@ EXPORT_SYMBOL(objagg_obj_put);
 
 /**
  * objagg_create - creates a new objagg instance
- * @ops:        user-specific callbacks
- * @priv:       pointer to a private data passed to the ops
+ * @ops:                user-specific callbacks
+ * @objagg_hints:       hints, can be NULL
+ * @priv:               pointer to a private data passed to the ops
  *
  * Note: all locking must be provided by the caller.
  *
@@ -374,18 +511,25 @@ EXPORT_SYMBOL(objagg_obj_put);
  * Returns a pointer to newly created objagg instance in case of success,
  * otherwise it returns pointer error using ERR_PTR macro.
  */
-struct objagg *objagg_create(const struct objagg_ops *ops, void *priv)
+struct objagg *objagg_create(const struct objagg_ops *ops,
+                             struct objagg_hints *objagg_hints, void *priv)
 {
         struct objagg *objagg;
         int err;
 
         if (WARN_ON(!ops || !ops->root_create || !ops->root_destroy ||
-                    !ops->delta_create || !ops->delta_destroy))
+                    !ops->delta_check || !ops->delta_create ||
+                    !ops->delta_destroy))
                 return ERR_PTR(-EINVAL);
+
         objagg = kzalloc(sizeof(*objagg), GFP_KERNEL);
         if (!objagg)
                 return ERR_PTR(-ENOMEM);
         objagg->ops = ops;
+        if (objagg_hints) {
+                objagg->hints = objagg_hints;
+                objagg_hints->refcount++;
+        }
         objagg->priv = priv;
         INIT_LIST_HEAD(&objagg->obj_list);
 
@@ -397,6 +541,8 @@ struct objagg *objagg_create(const struct objagg_ops *ops, void *priv)
         if (err)
                 goto err_rhashtable_init;
 
+        ida_init(&objagg->root_ida);
+
         trace_objagg_create(objagg);
         return objagg;
 
@@ -415,8 +561,11 @@ EXPORT_SYMBOL(objagg_create);
 void objagg_destroy(struct objagg *objagg)
 {
         trace_objagg_destroy(objagg);
+        ida_destroy(&objagg->root_ida);
         WARN_ON(!list_empty(&objagg->obj_list));
         rhashtable_destroy(&objagg->obj_ht);
+        if (objagg->hints)
+                objagg_hints_put(objagg->hints);
         kfree(objagg);
 }
 EXPORT_SYMBOL(objagg_destroy);
@@ -496,6 +645,404 @@ void objagg_stats_put(const struct objagg_stats *objagg_stats)
 }
 EXPORT_SYMBOL(objagg_stats_put);
 
+static struct objagg_hints_node *
+objagg_hints_node_create(struct objagg_hints *objagg_hints,
+                         struct objagg_obj *objagg_obj, size_t obj_size,
+                         struct objagg_hints_node *parent_hnode)
+{
+        unsigned int user_count = objagg_obj->stats.user_count;
+        struct objagg_hints_node *hnode;
+        int err;
+
+        hnode = kzalloc(sizeof(*hnode) + obj_size, GFP_KERNEL);
+        if (!hnode)
+                return ERR_PTR(-ENOMEM);
+        memcpy(hnode->obj, &objagg_obj->obj, obj_size);
+        hnode->stats_info.stats.user_count = user_count;
+        hnode->stats_info.stats.delta_user_count = user_count;
+        if (parent_hnode) {
+                parent_hnode->stats_info.stats.delta_user_count += user_count;
+        } else {
+                hnode->root_id = objagg_hints->root_count++;
+                hnode->stats_info.is_root = true;
+        }
+        hnode->stats_info.objagg_obj = objagg_obj;
+
+        err = rhashtable_insert_fast(&objagg_hints->node_ht, &hnode->ht_node,
+                                     objagg_hints->ht_params);
+        if (err)
+                goto err_ht_insert;
+
+        list_add(&hnode->list, &objagg_hints->node_list);
+        hnode->parent = parent_hnode;
+        objagg_hints->node_count++;
+
+        return hnode;
+
+err_ht_insert:
+        kfree(hnode);
+        return ERR_PTR(err);
+}
+
+static void objagg_hints_flush(struct objagg_hints *objagg_hints)
+{
+        struct objagg_hints_node *hnode, *tmp;
+
+        list_for_each_entry_safe(hnode, tmp, &objagg_hints->node_list, list) {
+                list_del(&hnode->list);
+                rhashtable_remove_fast(&objagg_hints->node_ht, &hnode->ht_node,
+                                       objagg_hints->ht_params);
+                kfree(hnode);
+        }
+}
+
+struct objagg_tmp_node {
+        struct objagg_obj *objagg_obj;
+        bool crossed_out;
+};
+
+struct objagg_tmp_graph {
+        struct objagg_tmp_node *nodes;
+        unsigned long nodes_count;
+        unsigned long *edges;
+};
+
+static int objagg_tmp_graph_edge_index(struct objagg_tmp_graph *graph,
+                                       int parent_index, int index)
+{
+        return index * graph->nodes_count + parent_index;
+}
+
+static void objagg_tmp_graph_edge_set(struct objagg_tmp_graph *graph,
+                                      int parent_index, int index)
+{
+        int edge_index = objagg_tmp_graph_edge_index(graph, index,
+                                                     parent_index);
+
+        __set_bit(edge_index, graph->edges);
+}
+
+static bool objagg_tmp_graph_is_edge(struct objagg_tmp_graph *graph,
+                                     int parent_index, int index)
+{
+        int edge_index = objagg_tmp_graph_edge_index(graph, index,
+                                                     parent_index);
+
+        return test_bit(edge_index, graph->edges);
+}
+
+static unsigned int objagg_tmp_graph_node_weight(struct objagg_tmp_graph *graph,
+                                                 unsigned int index)
+{
+        struct objagg_tmp_node *node = &graph->nodes[index];
+        unsigned int weight = node->objagg_obj->stats.user_count;
+        int j;
+
+        /* Node weight is sum of node users and all other nodes users
+         * that this node can represent with delta.
+         */
+
+        if (node->crossed_out)
+                return 0;
+        for (j = 0; j < graph->nodes_count; j++) {
+                if (!objagg_tmp_graph_is_edge(graph, index, j))
+                        continue;
+                node = &graph->nodes[j];
+                if (node->crossed_out)
+                        continue;
+                weight += node->objagg_obj->stats.user_count;
+        }
+        return weight;
+}
+
+static int objagg_tmp_graph_node_max_weight(struct objagg_tmp_graph *graph)
+{
+        unsigned int max_weight = 0;
+        unsigned int weight;
+        int max_index = -1;
+        int i;
+
+        for (i = 0; i < graph->nodes_count; i++) {
+                weight = objagg_tmp_graph_node_weight(graph, i);
+                if (weight > max_weight) {
+                        max_weight = weight;
+                        max_index = i;
+                }
+        }
+        return max_index;
+}
+
+static struct objagg_tmp_graph *objagg_tmp_graph_create(struct objagg *objagg)
+{
+        unsigned int nodes_count = objagg->obj_count;
+        struct objagg_tmp_graph *graph;
+        struct objagg_tmp_node *node;
+        struct objagg_tmp_node *pnode;
+        struct objagg_obj *objagg_obj;
+        size_t alloc_size;
+        int i, j;
+
+        graph = kzalloc(sizeof(*graph), GFP_KERNEL);
+        if (!graph)
+                return NULL;
+
+        graph->nodes = kcalloc(nodes_count, sizeof(*graph->nodes), GFP_KERNEL);
+        if (!graph->nodes)
+                goto err_nodes_alloc;
+        graph->nodes_count = nodes_count;
+
+        alloc_size = BITS_TO_LONGS(nodes_count * nodes_count) *
+                     sizeof(unsigned long);
+        graph->edges = kzalloc(alloc_size, GFP_KERNEL);
+        if (!graph->edges)
+                goto err_edges_alloc;
+
+        i = 0;
+        list_for_each_entry(objagg_obj, &objagg->obj_list, list) {
+                node = &graph->nodes[i++];
+                node->objagg_obj = objagg_obj;
+        }
+
+        /* Assemble a temporary graph. Insert edge X->Y in case Y can be
+         * in delta of X.
+         */
+        for (i = 0; i < nodes_count; i++) {
+                for (j = 0; j < nodes_count; j++) {
+                        if (i == j)
+                                continue;
+                        pnode = &graph->nodes[i];
+                        node = &graph->nodes[j];
+                        if (objagg->ops->delta_check(objagg->priv,
+                                                     pnode->objagg_obj->obj,
+                                                     node->objagg_obj->obj)) {
+                                objagg_tmp_graph_edge_set(graph, i, j);
+
+                        }
+                }
+        }
+        return graph;
+
+err_edges_alloc:
+        kfree(graph->nodes);
+err_nodes_alloc:
+        kfree(graph);
+        return NULL;
+}
+
+static void objagg_tmp_graph_destroy(struct objagg_tmp_graph *graph)
+{
+        kfree(graph->edges);
+        kfree(graph->nodes);
+        kfree(graph);
+}
+
+static int
+objagg_opt_simple_greedy_fillup_hints(struct objagg_hints *objagg_hints,
+                                      struct objagg *objagg)
+{
+        struct objagg_hints_node *hnode, *parent_hnode;
+        struct objagg_tmp_graph *graph;
+        struct objagg_tmp_node *node;
+        int index;
+        int j;
+        int err;
+
+        graph = objagg_tmp_graph_create(objagg);
+        if (!graph)
+                return -ENOMEM;
+
+        /* Find the nodes from the ones that can accommodate most users
+         * and cross them out of the graph. Save them to the hint list.
+         */
+        while ((index = objagg_tmp_graph_node_max_weight(graph)) != -1) {
+                node = &graph->nodes[index];
+                node->crossed_out = true;
+                hnode = objagg_hints_node_create(objagg_hints,
+                                                 node->objagg_obj,
+                                                 objagg->ops->obj_size,
+                                                 NULL);
+                if (IS_ERR(hnode)) {
+                        err = PTR_ERR(hnode);
+                        goto out;
+                }
+                parent_hnode = hnode;
+                for (j = 0; j < graph->nodes_count; j++) {
+                        if (!objagg_tmp_graph_is_edge(graph, index, j))
+                                continue;
+                        node = &graph->nodes[j];
+                        if (node->crossed_out)
+                                continue;
+                        node->crossed_out = true;
+                        hnode = objagg_hints_node_create(objagg_hints,
+                                                         node->objagg_obj,
+                                                         objagg->ops->obj_size,
+                                                         parent_hnode);
+                        if (IS_ERR(hnode)) {
+                                err = PTR_ERR(hnode);
+                                goto out;
+                        }
+                }
+        }
+
+        err = 0;
+out:
+        objagg_tmp_graph_destroy(graph);
+        return err;
+}
+
+struct objagg_opt_algo {
+        int (*fillup_hints)(struct objagg_hints *objagg_hints,
+                            struct objagg *objagg);
+};
+
+static const struct objagg_opt_algo objagg_opt_simple_greedy = {
+        .fillup_hints = objagg_opt_simple_greedy_fillup_hints,
+};
+
+
+static const struct objagg_opt_algo *objagg_opt_algos[] = {
+        [OBJAGG_OPT_ALGO_SIMPLE_GREEDY] = &objagg_opt_simple_greedy,
+};
+
+static int objagg_hints_obj_cmp(struct rhashtable_compare_arg *arg,
+                                const void *obj)
+{
+        struct rhashtable *ht = arg->ht;
+        struct objagg_hints *objagg_hints =
+                        container_of(ht, struct objagg_hints, node_ht);
+        const struct objagg_ops *ops = objagg_hints->ops;
+        const char *ptr = obj;
+
+        ptr += ht->p.key_offset;
+        return ops->hints_obj_cmp ? ops->hints_obj_cmp(ptr, arg->key) :
+                                    memcmp(ptr, arg->key, ht->p.key_len);
+}
+
+/**
+ * objagg_hints_get - obtains hints instance
+ * @objagg:             objagg instance
+ * @opt_algo_type:      type of hints finding algorithm
+ *
+ * Note: all locking must be provided by the caller.
+ *
+ * According to the algo type, the existing objects of objagg instance
+ * are going to be went-through to assemble an optimal tree. We call this
+ * tree hints. These hints can be later on used for creation of
+ * a new objagg instance. There, the future object creations are going
+ * to be consulted with these hints in order to find out, where exactly
+ * the new object should be put as a root or delta.
+ *
+ * Returns a pointer to hints instance in case of success,
+ * otherwise it returns pointer error using ERR_PTR macro.
+ */
+struct objagg_hints *objagg_hints_get(struct objagg *objagg,
+                                      enum objagg_opt_algo_type opt_algo_type)
+{
+        const struct objagg_opt_algo *algo = objagg_opt_algos[opt_algo_type];
+        struct objagg_hints *objagg_hints;
+        int err;
+
+        objagg_hints = kzalloc(sizeof(*objagg_hints), GFP_KERNEL);
+        if (!objagg_hints)
+                return ERR_PTR(-ENOMEM);
+
+        objagg_hints->ops = objagg->ops;
+        objagg_hints->refcount = 1;
+
+        INIT_LIST_HEAD(&objagg_hints->node_list);
+
+        objagg_hints->ht_params.key_len = objagg->ops->obj_size;
+        objagg_hints->ht_params.key_offset =
+                                offsetof(struct objagg_hints_node, obj);
+        objagg_hints->ht_params.head_offset =
+                                offsetof(struct objagg_hints_node, ht_node);
+        objagg_hints->ht_params.obj_cmpfn = objagg_hints_obj_cmp;
+
+        err = rhashtable_init(&objagg_hints->node_ht, &objagg_hints->ht_params);
+        if (err)
+                goto err_rhashtable_init;
+
+        err = algo->fillup_hints(objagg_hints, objagg);
+        if (err)
+                goto err_fillup_hints;
+
+        if (WARN_ON(objagg_hints->node_count != objagg->obj_count))
+                goto err_node_count_check;
+
+        return objagg_hints;
+
+err_node_count_check:
+err_fillup_hints:
+        objagg_hints_flush(objagg_hints);
+        rhashtable_destroy(&objagg_hints->node_ht);
+err_rhashtable_init:
+        kfree(objagg_hints);
+        return ERR_PTR(err);
+}
+EXPORT_SYMBOL(objagg_hints_get);
+
+/**
+ * objagg_hints_put - puts hints instance
+ * @objagg_hints:       objagg hints instance
+ *
+ * Note: all locking must be provided by the caller.
+ */
+void objagg_hints_put(struct objagg_hints *objagg_hints)
+{
+        if (--objagg_hints->refcount)
+                return;
+        objagg_hints_flush(objagg_hints);
+        rhashtable_destroy(&objagg_hints->node_ht);
+        kfree(objagg_hints);
+}
+EXPORT_SYMBOL(objagg_hints_put);
+
+/**
+ * objagg_hints_stats_get - obtains stats of the hints instance
+ * @objagg_hints:       hints instance
+ *
+ * Note: all locking must be provided by the caller.
+ *
+ * The returned structure contains statistics of all objects
+ * currently in use, ordered by following rules:
+ * 1) Root objects are always on lower indexes than the rest.
+ * 2) Objects with higher delta user count are always on lower
+ *    indexes.
+ * 3) In case multiple objects have the same delta user count,
+ *    the objects are ordered by user count.
+ *
+ * Returns a pointer to stats instance in case of success,
+ * otherwise it returns pointer error using ERR_PTR macro.
+ */
+const struct objagg_stats *
+objagg_hints_stats_get(struct objagg_hints *objagg_hints)
+{
+        struct objagg_stats *objagg_stats;
+        struct objagg_hints_node *hnode;
+        int i;
+
+        objagg_stats = kzalloc(struct_size(objagg_stats, stats_info,
+                                           objagg_hints->node_count),
+                               GFP_KERNEL);
+        if (!objagg_stats)
+                return ERR_PTR(-ENOMEM);
+
+        i = 0;
+        list_for_each_entry(hnode, &objagg_hints->node_list, list) {
+                memcpy(&objagg_stats->stats_info[i], &hnode->stats_info,
+                       sizeof(objagg_stats->stats_info[0]));
+                i++;
+        }
+        objagg_stats->stats_info_count = i;
+
+        sort(objagg_stats->stats_info, objagg_stats->stats_info_count,
+             sizeof(struct objagg_obj_stats_info),
+             objagg_stats_info_sort_cmp_func, NULL);
+
+        return objagg_stats;
+}
+EXPORT_SYMBOL(objagg_hints_stats_get);
+
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_AUTHOR("Jiri Pirko <jiri@mellanox.com>");
 MODULE_DESCRIPTION("Object aggregation manager");
diff --git a/lib/test_objagg.c b/lib/test_objagg.c
index ab57144bb0cd..3744573b6365 100644
--- a/lib/test_objagg.c
+++ b/lib/test_objagg.c
@@ -87,6 +87,15 @@ static void world_obj_put(struct world *world, struct objagg *objagg,
 
 #define MAX_KEY_ID_DIFF 5
 
+static bool delta_check(void *priv, const void *parent_obj, const void *obj)
+{
+        const struct tokey *parent_key = parent_obj;
+        const struct tokey *key = obj;
+        int diff = key->id - parent_key->id;
+
+        return diff >= 0 && diff <= MAX_KEY_ID_DIFF;
+}
+
 static void *delta_create(void *priv, void *parent_obj, void *obj)
 {
         struct tokey *parent_key = parent_obj;
@@ -95,7 +104,7 @@ static void *delta_create(void *priv, void *parent_obj, void *obj)
         int diff = key->id - parent_key->id;
         struct delta *delta;
 
-        if (diff < 0 || diff > MAX_KEY_ID_DIFF)
+        if (!delta_check(priv, parent_obj, obj))
                 return ERR_PTR(-EINVAL);
 
         delta = kzalloc(sizeof(*delta), GFP_KERNEL);
@@ -115,7 +124,7 @@ static void delta_destroy(void *priv, void *delta_priv)
         kfree(delta);
 }
 
-static void *root_create(void *priv, void *obj)
+static void *root_create(void *priv, void *obj, unsigned int id)
 {
         struct world *world = priv;
         struct tokey *key = obj;
@@ -268,6 +277,12 @@ stats_put:
         return err;
 }
 
+static bool delta_check_dummy(void *priv, const void *parent_obj,
+                              const void *obj)
+{
+        return false;
+}
+
 static void *delta_create_dummy(void *priv, void *parent_obj, void *obj)
 {
         return ERR_PTR(-EOPNOTSUPP);
@@ -279,6 +294,7 @@ static void delta_destroy_dummy(void *priv, void *delta_priv)
 
 static const struct objagg_ops nodelta_ops = {
         .obj_size = sizeof(struct tokey),
+        .delta_check = delta_check_dummy,
         .delta_create = delta_create_dummy,
         .delta_destroy = delta_destroy_dummy,
         .root_create = root_create,
@@ -292,7 +308,7 @@ static int test_nodelta(void)
         int i;
         int err;
 
-        objagg = objagg_create(&nodelta_ops, &world);
+        objagg = objagg_create(&nodelta_ops, NULL, &world);
         if (IS_ERR(objagg))
                 return PTR_ERR(objagg);
 
@@ -357,6 +373,7 @@ err_stats_second_zero:
 
 static const struct objagg_ops delta_ops = {
         .obj_size = sizeof(struct tokey),
+        .delta_check = delta_check,
         .delta_create = delta_create,
         .delta_destroy = delta_destroy,
         .root_create = root_create,
@@ -793,7 +810,7 @@ static int test_delta(void)
         int i;
         int err;
 
-        objagg = objagg_create(&delta_ops, &world);
+        objagg = objagg_create(&delta_ops, NULL, &world);
         if (IS_ERR(objagg))
                 return PTR_ERR(objagg);
 
@@ -815,6 +832,170 @@ err_do_action_item:
         return err;
 }
 
+struct hints_case {
+        const unsigned int *key_ids;
+        size_t key_ids_count;
+        struct expect_stats expect_stats;
+        struct expect_stats expect_stats_hints;
+};
+
+static const unsigned int hints_case_key_ids[] = {
+        1, 7, 3, 5, 3, 1, 30, 8, 8, 5, 6, 8,
+};
+
+static const struct hints_case hints_case = {
+        .key_ids = hints_case_key_ids,
+        .key_ids_count = ARRAY_SIZE(hints_case_key_ids),
+        .expect_stats =
+                EXPECT_STATS(7, ROOT(1, 2, 7), ROOT(7, 1, 4), ROOT(30, 1, 1),
+                                DELTA(8, 3), DELTA(3, 2),
+                                DELTA(5, 2), DELTA(6, 1)),
+        .expect_stats_hints =
+                EXPECT_STATS(7, ROOT(3, 2, 9), ROOT(1, 2, 2), ROOT(30, 1, 1),
+                                DELTA(8, 3), DELTA(5, 2),
+                                DELTA(6, 1), DELTA(7, 1)),
+};
+
+static void __pr_debug_stats(const struct objagg_stats *stats)
+{
+        int i;
+
+        for (i = 0; i < stats->stats_info_count; i++)
+                pr_debug("Stat index %d key %u: u %d, d %d, %s\n", i,
+                         obj_to_key_id(stats->stats_info[i].objagg_obj),
+                         stats->stats_info[i].stats.user_count,
+                         stats->stats_info[i].stats.delta_user_count,
+                         stats->stats_info[i].is_root ? "root" : "noroot");
+}
+
+static void pr_debug_stats(struct objagg *objagg)
+{
+        const struct objagg_stats *stats;
+
+        stats = objagg_stats_get(objagg);
+        if (IS_ERR(stats))
+                return;
+        __pr_debug_stats(stats);
+        objagg_stats_put(stats);
+}
+
+static void pr_debug_hints_stats(struct objagg_hints *objagg_hints)
+{
+        const struct objagg_stats *stats;
+
+        stats = objagg_hints_stats_get(objagg_hints);
+        if (IS_ERR(stats))
+                return;
+        __pr_debug_stats(stats);
+        objagg_stats_put(stats);
+}
+
+static int check_expect_hints_stats(struct objagg_hints *objagg_hints,
+                                    const struct expect_stats *expect_stats,
+                                    const char **errmsg)
+{
+        const struct objagg_stats *stats;
+        int err;
+
+        stats = objagg_hints_stats_get(objagg_hints);
+        if (IS_ERR(stats))
+                return PTR_ERR(stats);
+        err = __check_expect_stats(stats, expect_stats, errmsg);
+        objagg_stats_put(stats);
+        return err;
+}
+
+static int test_hints_case(const struct hints_case *hints_case)
+{
+        struct objagg_obj *objagg_obj;
+        struct objagg_hints *hints;
+        struct world world2 = {};
+        struct world world = {};
+        struct objagg *objagg2;
+        struct objagg *objagg;
+        const char *errmsg;
+        int i;
+        int err;
+
+        objagg = objagg_create(&delta_ops, NULL, &world);
+        if (IS_ERR(objagg))
+                return PTR_ERR(objagg);
+
+        for (i = 0; i < hints_case->key_ids_count; i++) {
+                objagg_obj = world_obj_get(&world, objagg,
+                                           hints_case->key_ids[i]);
+                if (IS_ERR(objagg_obj)) {
+                        err = PTR_ERR(objagg_obj);
+                        goto err_world_obj_get;
+                }
+        }
+
+        pr_debug_stats(objagg);
+        err = check_expect_stats(objagg, &hints_case->expect_stats, &errmsg);
+        if (err) {
+                pr_err("Stats: %s\n", errmsg);
+                goto err_check_expect_stats;
+        }
+
+        hints = objagg_hints_get(objagg, OBJAGG_OPT_ALGO_SIMPLE_GREEDY);
+        if (IS_ERR(hints)) {
+                err = PTR_ERR(hints);
+                goto err_hints_get;
+        }
+
+        pr_debug_hints_stats(hints);
+        err = check_expect_hints_stats(hints, &hints_case->expect_stats_hints,
+                                       &errmsg);
+        if (err) {
+                pr_err("Hints stats: %s\n", errmsg);
+                goto err_check_expect_hints_stats;
+        }
+
+        objagg2 = objagg_create(&delta_ops, hints, &world2);
+        if (IS_ERR(objagg))
+                return PTR_ERR(objagg);
+
+        for (i = 0; i < hints_case->key_ids_count; i++) {
+                objagg_obj = world_obj_get(&world2, objagg2,
+                                           hints_case->key_ids[i]);
+                if (IS_ERR(objagg_obj)) {
+                        err = PTR_ERR(objagg_obj);
+                        goto err_world2_obj_get;
+                }
+        }
+
+        pr_debug_stats(objagg2);
+        err = check_expect_stats(objagg2, &hints_case->expect_stats_hints,
+                                 &errmsg);
+        if (err) {
+                pr_err("Stats2: %s\n", errmsg);
+                goto err_check_expect_stats2;
+        }
+
+        err = 0;
+
+err_check_expect_stats2:
+err_world2_obj_get:
+        for (i--; i >= 0; i--)
+                world_obj_put(&world2, objagg, hints_case->key_ids[i]);
+        objagg_hints_put(hints);
+        objagg_destroy(objagg2);
+        i = hints_case->key_ids_count;
+err_check_expect_hints_stats:
+err_hints_get:
+err_check_expect_stats:
+err_world_obj_get:
+        for (i--; i >= 0; i--)
+                world_obj_put(&world, objagg, hints_case->key_ids[i]);
+
+        objagg_destroy(objagg);
+        return err;
+}
+static int test_hints(void)
+{
+        return test_hints_case(&hints_case);
+}
+
 static int __init test_objagg_init(void)
 {
         int err;
@@ -822,7 +1003,10 @@ static int __init test_objagg_init(void)
         err = test_nodelta();
         if (err)
                 return err;
-        return test_delta();
+        err = test_delta();
+        if (err)
+                return err;
+        return test_hints();
 }
 
 static void __exit test_objagg_exit(void)