From cced51cbd23aa732f0243fe555b4427ff46267b4 Mon Sep 17 00:00:00 2001
From: Scott Shawcroft <scott@tannewt.org>
Date: Thu, 28 Jun 2018 10:43:39 -0700
Subject: [PATCH] Limit qstr pool size to reduce memory waste.

---
 py/mpconfig.h |  6 ++++++
 py/qstr.c     | 10 +++++++---
 2 files changed, 13 insertions(+), 3 deletions(-)
 mode change 100644 => 100755 py/mpconfig.h
 mode change 100644 => 100755 py/qstr.c

diff --git a/py/mpconfig.h b/py/mpconfig.h
old mode 100644
new mode 100755
index 765ae1e8f0..74d7c2c929
--- 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
old mode 100644
new mode 100755
index 49b2d9daaa..de4dc6240a
--- 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);