Introduced the option MEM_USE_POOLS to use 4 pools with different sized elements instead of a heap. This both prevents memory fragmentation and gives a higher speed at the cost of more memory consumption. Turned off by default.

src/include/lwip/mem.h

@@ -66,11 +66,21 @@ typedef u16_t mem_size_t;
 #define mem_realloc(x, size) realloc(x,size)
 #endif
 #else /* MEM_LIBC_MALLOC */
+#if MEM_USE_POOLS
+/** The pool implementation of the heap currently uses 4 pools */
+#define MEM_POOL_COUNT   4
+/** mem_init is not used when using pools instead of a heap */
+#define mem_init()
+/** mem_realloc is not used when using pools instead of a heap:
+    we can't free part of a pool element and don't want to copy the rest */
+#define mem_realloc(mem, size) (mem)
+#else /* MEM_USE_POOLS */
 /* lwIP alternative malloc */
 void  mem_init(void);
+void *mem_realloc(void *mem, mem_size_t size);
+#endif /* MEM_USE_POOLS */
 void *mem_malloc(mem_size_t size);
 void  mem_free(void *mem);
-void *mem_realloc(void *mem, mem_size_t size);
 #endif /* MEM_LIBC_MALLOC */
 
 #ifndef LWIP_MEM_ALIGN_SIZE

src/include/lwip/memp.h

@@ -56,6 +56,12 @@ typedef enum {
 #endif
   MEMP_PBUF_POOL,
   MEMP_SYS_TIMEOUT,
+#if MEM_USE_POOLS
+  MEMP_MEM_POOL_1,
+  MEMP_MEM_POOL_2,
+  MEMP_MEM_POOL_3,
+  MEMP_MEM_POOL_4,
+#endif
 
   MEMP_MAX
 } memp_t;
@@ -70,6 +76,10 @@ void *memp_malloc(memp_t type);
 #endif
 void  memp_free(memp_t type, void *mem);
 
+#if MEM_USE_POOLS
+extern const u16_t memp_sizes[MEMP_MAX];
+#endif
+
 #ifdef __cplusplus
 }
 #endif

src/include/lwip/opt.h

@@ -66,6 +66,8 @@
 #endif
 
 /* ---------- Memory options ---------- */
+/* Use malloc/free/realloc provided by your C-library instead of the
+   lwip internal allocator. Can save code size if you already use it. */
 #ifndef MEM_LIBC_MALLOC
 #define MEM_LIBC_MALLOC                 0
 #endif
@@ -73,13 +75,51 @@
 /* MEM_ALIGNMENT: should be set to the alignment of the CPU for which
    lwIP is compiled. 4 byte alignment -> define MEM_ALIGNMENT to 4, 2
    byte alignment -> define MEM_ALIGNMENT to 2. */
-
 #ifndef MEM_ALIGNMENT
 #define MEM_ALIGNMENT                   1
 #endif
 
+/* Memory can be allocated from 4 pools with element of different size.
+   When mem_malloc is called, and element of the smallest pool that can
+   provide the lenght needed is returned. */
+#ifndef MEM_USE_POOLS
+#define MEM_USE_POOLS                   0
+#endif
+
+#if MEM_USE_POOLS
+/* The element sizes of the 4 pools.
+   The sizes must be increasing, e.g. the elements in pool 2 must be
+   bigger than the elements in pool 1 and so on. If this is not the case,
+   mem_malloc will not work correctly. */
+#ifndef MEM_POOL_SIZE_1
+#error You must have at least one pool if MEM_USE_POOLS is set to 1!
+#endif
+#ifndef MEM_POOL_SIZE_2
+#define MEM_POOL_SIZE_2                 0
+#endif
+#ifndef MEM_POOL_SIZE_3
+#define MEM_POOL_SIZE_3                 0
+#endif
+#ifndef MEM_POOL_SIZE_4
+#define MEM_POOL_SIZE_4                 0
+#endif
+/* The element count of the 4 pools */
+#ifndef MEM_POOL_NUM_1
+#error You must have at least one pool if MEM_USE_POOLS is set to 1!
+#endif
+#ifndef MEM_POOL_NUM_2
+#define MEM_POOL_NUM_2                  0
+#endif
+#ifndef MEM_POOL_NUM_3
+#define MEM_POOL_NUM_3                  0
+#endif
+#ifndef MEM_POOL_NUM_4
+#define MEM_POOL_NUM_4                  0
+#endif
+#endif
+
 /* MEM_SIZE: the size of the heap memory. If the application will send
-a lot of data that needs to be copied, this should be set high. */
+   a lot of data that needs to be copied, this should be set high. */
 #ifndef MEM_SIZE
 #define MEM_SIZE                        1600
 #endif