Limit qstr pool size to reduce memory waste.

tannewt · tannewt · commit cced51cbd23a · 2018-07-03T05:45:51.000-07:00
diff --git a/py/mpconfig.h b/py/mpconfig.h
@@ -130,6 +130,12 @@
 #define MICROPY_ALLOC_QSTR_CHUNK_INIT (128)
 #endif
 
+// Max number of entries in newly allocated QSTR pools. Smaller numbers may make QSTR lookups
+// slightly slower but reduce the waste of unused spots.
+#ifndef MICROPY_QSTR_POOL_MAX_ENTRIES
+#define MICROPY_QSTR_POOL_MAX_ENTRIES (64)
+#endif
+
 // Initial amount for lexer indentation level
 #ifndef MICROPY_ALLOC_LEXER_INDENT_INIT
 #define MICROPY_ALLOC_LEXER_INDENT_INIT (10)
diff --git a/py/qstr.c b/py/qstr.c
@@ -144,14 +144,18 @@ STATIC qstr qstr_add(const byte *q_ptr) {
 
     // make sure we have room in the pool for a new qstr
     if (MP_STATE_VM(last_pool)->len >= MP_STATE_VM(last_pool)->alloc) {
-        qstr_pool_t *pool = m_new_ll_obj_var_maybe(qstr_pool_t, const char*, MP_STATE_VM(last_pool)->alloc * 2);
+        uint32_t new_pool_length = MP_STATE_VM(last_pool)->alloc * 2;
+        if (new_pool_length > MICROPY_QSTR_POOL_MAX_ENTRIES) {
+            new_pool_length = MICROPY_QSTR_POOL_MAX_ENTRIES;
+        }
+        qstr_pool_t *pool = m_new_ll_obj_var_maybe(qstr_pool_t, const char*, new_pool_length);
         if (pool == NULL) {
             QSTR_EXIT();
-            m_malloc_fail(MP_STATE_VM(last_pool)->alloc * 2);
+            m_malloc_fail(new_pool_length);
         }
         pool->prev = MP_STATE_VM(last_pool);
         pool->total_prev_len = MP_STATE_VM(last_pool)->total_prev_len + MP_STATE_VM(last_pool)->len;
-        pool->alloc = MP_STATE_VM(last_pool)->alloc * 2;
+        pool->alloc = new_pool_length;
         pool->len = 0;
         MP_STATE_VM(last_pool) = pool;
         DEBUG_printf("QSTR: allocate new pool of size %d\n", MP_STATE_VM(last_pool)->alloc);
