maple_tree: Add single node allocation support to maple state

The fast path through a write will require replacing a single node in
the tree.  Using a sheaf (32 nodes) is too heavy for the fast path, so
special case the node store operation by just allocating one node in the
maple state.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>

diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
index 9a53e527297ebf40456febfb59908b9146283c9f..09d49781d150ad0fe8c7a94317d068ea3673ff75 100644 (file)
--- a/include/linux/maple_tree.h
+++ b/include/linux/maple_tree.h
@@ -443,6 +443,7 @@ struct ma_state {
        unsigned long min;              /* The minimum index of this node - implied pivot min */
        unsigned long max;              /* The maximum index of this node - implied pivot max */
        struct slab_sheaf *sheaf;       /* Allocated nodes for this operation */
+       struct maple_node *alloc;       /* allocated nodes */
        unsigned long node_request;
        enum maple_status status;       /* The status of the state (active, start, none, etc) */
        unsigned char depth;            /* depth of tree descent during write */
@@ -491,8 +492,9 @@ struct ma_wr_state {
                .status = ma_start,                                     \
                .min = 0,                                               \
                .max = ULONG_MAX,                                       \
-               .node_request= 0,                                       \
                .sheaf = NULL,                                          \
+               .alloc = NULL,                                          \
+               .node_request= 0,                                       \
                .mas_flags = 0,                                         \
                .store_type = wr_invalid,                               \
        }

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index ff664265946ce51ced6e69acb7562cb0bcd575ba..5b8f4ac791d764019402afe906f0a713d66ac3eb 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1101,16 +1101,23 @@ static int mas_ascend(struct ma_state *mas)
  *
  * Return: A pointer to a maple node.
  */
-static inline struct maple_node *mas_pop_node(struct ma_state *mas)
+static __always_inline struct maple_node *mas_pop_node(struct ma_state *mas)
 {
        struct maple_node *ret;
 
+       if (mas->alloc) {
+               ret = mas->alloc;
+               mas->alloc = NULL;
+               goto out;
+       }
+
        if (WARN_ON_ONCE(!mas->sheaf))
                return NULL;
 
        ret = kmem_cache_alloc_from_sheaf(maple_node_cache, GFP_NOWAIT, mas->sheaf);
-       memset(ret, 0, sizeof(*ret));
 
+out:
+       memset(ret, 0, sizeof(*ret));
        return ret;
 }
 
@@ -1121,9 +1128,34 @@ static inline struct maple_node *mas_pop_node(struct ma_state *mas)
  */
 static inline void mas_alloc_nodes(struct ma_state *mas, gfp_t gfp)
 {
-       if (unlikely(mas->sheaf)) {
-               unsigned long refill = mas->node_request;
+       if (!mas->node_request)
+               return;
+
+       if (mas->node_request == 1) {
+               if (mas->sheaf)
+                       goto use_sheaf;
+
+               if (mas->alloc)
+                       return;
 
+               mas->alloc = mt_alloc_one(gfp);
+               if (!mas->alloc)
+                       goto error;
+
+               mas->node_request = 0;
+               return;
+       }
+
+use_sheaf:
+       if (unlikely(mas->alloc)) {
+               mt_free_one(mas->alloc);
+               mas->alloc = NULL;
+       }
+
+       if (mas->sheaf) {
+               unsigned long refill;
+
+               refill = mas->node_request;
                if(kmem_cache_sheaf_size(mas->sheaf) >= refill) {
                        mas->node_request = 0;
                        return;
@@ -5392,8 +5424,11 @@ void mas_destroy(struct ma_state *mas)
        mas->node_request = 0;
        if (mas->sheaf)
                mt_return_sheaf(mas->sheaf);
-
        mas->sheaf = NULL;
+
+       if (mas->alloc)
+               mt_free_one(mas->alloc);
+       mas->alloc = NULL;
 }
 EXPORT_SYMBOL_GPL(mas_destroy);
 
@@ -6080,7 +6115,7 @@ bool mas_nomem(struct ma_state *mas, gfp_t gfp)
                mas_alloc_nodes(mas, gfp);
        }
 
-       if (!mas->sheaf)
+       if (!mas->sheaf && !mas->alloc)
                return false;
 
        mas->status = ma_start;