eina: introduce an API for requesting memory near already allocated memory from an Eina_Mempool.

Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Differential Revision: https://phab.enlightenment.org/D10535

src/lib/eina/eina_inline_mempool.x

@@ -61,6 +61,11 @@ struct _Eina_Mempool_Backend
     * @use eina_mempool_iterator_new
     */
    Eina_Iterator *(*iterator)(void *data);
+   /** Function to allocate memory near already allocated memory.
+    * @since 1.24
+    * @use eina_mempool_malloc_near
+    */
+   void *(*alloc_near)(void *data, void *after, void *before, unsigned int size);
 };
 
 struct _Eina_Mempool_Backend_ABI1
@@ -80,6 +85,7 @@ struct _Eina_Mempool_Backend_ABI2
    void (*repack)(void *data, Eina_Mempool_Repack_Cb cb, void *cb_data);
    Eina_Bool (*from)(void *data, void *element);
    Eina_Iterator *(*iterator)(void *data);
+   void *(*alloc_near)(void *data, void *after, void *before, unsigned int size);
 };
 
 struct _Eina_Mempool
@@ -101,6 +107,14 @@ eina_mempool_malloc(Eina_Mempool *mp, unsigned int size)
    return mp->backend.alloc(mp->backend_data, size);
 }
 
+static inline void *
+eina_mempool_malloc_near(Eina_Mempool *mp, void *after, void *before, unsigned int size)
+{
+   if (mp->backend2 && mp->backend2->alloc_near && (!(after == NULL && before == NULL)))
+     return mp->backend2->alloc_near(mp->backend_data, after, before, size);
+   return mp->backend.alloc(mp->backend_data, size);
+}
+
 static inline void *
 eina_mempool_calloc(Eina_Mempool *mp, unsigned int size)
 {

src/lib/eina/eina_mempool.c

@@ -98,13 +98,14 @@ _new_va(const char *name,
    SBP(shutdown);
 #undef SBP
 
-   if (be->repack || be->from)
+   if (be->repack || be->from || be->iterator || be->alloc_near)
      {
         mp->backend2 = calloc(1, sizeof (Eina_Mempool_Backend_ABI2));
         if (!mp->backend2) goto on_error;
         mp->backend2->repack = be->repack;
         mp->backend2->from = be->from;
         mp->backend2->iterator = be->iterator;
+        mp->backend2->alloc_near = be->alloc_near;
      }
 
    mp->backend_data = mp->backend.init(context, options, args);

src/lib/eina/eina_mempool.h

@@ -124,6 +124,29 @@ static inline void *eina_mempool_realloc(Eina_Mempool *mp, void *element, unsign
  */
 static inline void *eina_mempool_malloc(Eina_Mempool *mp, unsigned int size) EINA_MALLOC EINA_ARG_NONNULL(1) EINA_WARN_UNUSED_RESULT;
 
+/**
+ * @brief Allocates memory in the given mempool using locality hint to improve future memory access use.
+ *
+ * @param[in] mp The mempool
+ * @param[in] after Hint to the nearest pointer after which to try find an empty spot.
+ * @param[in] before Hint to the nearest pointer before which to try find an empty spot.
+ * @param[in] size The size in bytes to allocate
+ * @return The newly allocated data that might be near @p after and @p before.
+ *
+ * This function is to be used to improve cache locality of structure that are likely to be used
+ * one after another. An example of this use would be Eina_List.
+ *
+ * @note This function allocates and returns @p size bytes using the mempool @p mp.
+ *       If not used anymore, the data must be freed with eina_mempool_free().
+ * @note @p after and @p before must be either @c NULL or allocated by the same mempool
+ *       @p mp. They are hint and if no space near them is found, memory will be allocated
+ *       without locality improvement.
+ * @warning No checks are done for @p mp.
+ *
+ * @see eina_mempool_free()
+ */
+static inline void *eina_mempool_malloc_near(Eina_Mempool *mp, void *after, void *before, unsigned int size) EINA_WARN_UNUSED_RESULT;
+
 /**
  * @brief Allocates and zeros memory using the given mempool.
  *

src/modules/eina/mp/chained_pool/eina_chained_mempool.c

@@ -726,7 +726,8 @@ static Eina_Mempool_Backend _eina_chained_mp_backend = {
    &eina_chained_mempool_shutdown,
    &eina_chained_mempool_repack,
    &eina_chained_mempool_from,
-   &eina_chained_mempool_iterator_new
+   &eina_chained_mempool_iterator_new,
+   NULL
 };
 
 Eina_Bool chained_init(void)

src/modules/eina/mp/one_big/eina_one_big.c

@@ -452,7 +452,8 @@ static Eina_Mempool_Backend _eina_one_big_mp_backend = {
    &eina_one_big_shutdown,
    NULL,
    &eina_one_big_from,
-   &eina_one_big_iterator_new
+   &eina_one_big_iterator_new,
+   NULL
 };
 
 Eina_Bool one_big_init(void)

src/modules/eina/mp/pass_through/eina_pass_through.c

@@ -77,6 +77,7 @@ static Eina_Mempool_Backend _eina_pass_through_mp_backend = {
    &eina_pass_through_shutdown,
    NULL,
    &eina_pass_through_from,
+   NULL,
    NULL
 };