diff --git a/src/array.c b/src/array.c
index d8ecf73c8dadf..47eb5e782a3be 100644
--- a/src/array.c
+++ b/src/array.c
@@ -514,32 +514,39 @@ JL_DLLEXPORT jl_value_t *jl_array_to_string(jl_array_t *a)
     return jl_pchar_to_string((const char*)jl_array_data(a), len);
 }
 
-JL_DLLEXPORT jl_value_t *jl_pchar_to_string(const char *str, size_t len)
+JL_DLLEXPORT jl_value_t *jl_alloc_string(size_t len)
 {
+    if (len == 0)
+        return jl_an_empty_string;
     size_t sz = sizeof(size_t) + len + 1; // add space for trailing \nul protector and size
     if (sz < len) // overflow
         jl_throw(jl_memory_exception);
-    if (len == 0)
-        return jl_an_empty_string;
     jl_task_t *ct = jl_current_task;
-    jl_value_t *s = jl_gc_alloc_(ct->ptls, sz, jl_string_type); // force inlining
+    jl_value_t *s;
+    jl_ptls_t ptls = ct->ptls;
+    const size_t allocsz = sz + sizeof(jl_taggedvalue_t);
+    if (sz <= GC_MAX_SZCLASS) {
+        int pool_id = jl_gc_szclass_align8(allocsz);
+        jl_gc_pool_t *p = &ptls->heap.norm_pools[pool_id];
+        int osize = jl_gc_sizeclasses[pool_id];
+        s = jl_gc_pool_alloc(ptls, (char*)p - (char*)ptls, osize);
+    }
+    else {
+        if (allocsz < sz) // overflow in adding offs, size was "negative"
+            jl_throw(jl_memory_exception);
+        s = jl_gc_big_alloc(ptls, allocsz);
+    }
+    jl_set_typeof(s, jl_string_type);
     *(size_t*)s = len;
-    memcpy((char*)s + sizeof(size_t), str, len);
-    ((char*)s + sizeof(size_t))[len] = 0;
+    jl_string_data(s)[len] = 0;
     return s;
 }
 
-JL_DLLEXPORT jl_value_t *jl_alloc_string(size_t len)
+JL_DLLEXPORT jl_value_t *jl_pchar_to_string(const char *str, size_t len)
 {
-    size_t sz = sizeof(size_t) + len + 1; // add space for trailing \nul protector and size
-    if (sz < len) // overflow
-        jl_throw(jl_memory_exception);
-    if (len == 0)
-        return jl_an_empty_string;
-    jl_task_t *ct = jl_current_task;
-    jl_value_t *s = jl_gc_alloc_(ct->ptls, sz, jl_string_type); // force inlining
-    *(size_t*)s = len;
-    ((char*)s + sizeof(size_t))[len] = 0;
+    jl_value_t *s = jl_alloc_string(len);
+    if (len > 0)
+        memcpy(jl_string_data(s), str, len);
     return s;
 }
 
diff --git a/src/gc.c b/src/gc.c
index 5429510f08651..3734ec40d0795 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -3286,9 +3286,6 @@ void jl_init_thread_heap(jl_ptls_t ptls)
     jl_thread_heap_t *heap = &ptls->heap;
     jl_gc_pool_t *p = heap->norm_pools;
     for (int i = 0; i < JL_GC_N_POOLS; i++) {
-        assert((jl_gc_sizeclasses[i] < 16 &&
-                jl_gc_sizeclasses[i] % sizeof(void*) == 0) ||
-               (jl_gc_sizeclasses[i] % 16 == 0));
         p[i].osize = jl_gc_sizeclasses[i];
         p[i].freelist = NULL;
         p[i].newpages = NULL;
diff --git a/src/julia_internal.h b/src/julia_internal.h
index 2f14e3ad6832b..c9ff2716530eb 100644
--- a/src/julia_internal.h
+++ b/src/julia_internal.h
@@ -247,12 +247,15 @@ static const int jl_gc_sizeclasses[] = {
     4, 8, 12,
 #endif
 
-    // 16 pools at 16-byte spacing
-    16, 32, 48, 64, 80, 96, 112, 128,
+    // 16 pools at 8-byte spacing
+    // the 8-byte aligned pools are only used for Strings
+    16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96, 104, 112, 120, 128, 136,
+    // 8 pools at 16-byte spacing
     144, 160, 176, 192, 208, 224, 240, 256,
 
     // the following tables are computed for maximum packing efficiency via the formula:
-    // sz=(div(2^14-8,rng)÷16)*16; hcat(sz, (2^14-8)÷sz, 2^14-(2^14-8)÷sz.*sz)'
+    // pg = 2^14
+    // sz = (div.(pg-8, rng).÷16)*16; hcat(sz, (pg-8).÷sz, pg .- (pg-8).÷sz.*sz)'
 
     // rng = 60:-4:32 (8 pools)
     272, 288, 304, 336, 368, 400, 448, 496,
@@ -293,15 +296,14 @@ STATIC_INLINE int jl_gc_alignment(size_t sz)
 }
 JL_DLLEXPORT int jl_alignment(size_t sz);
 
-// the following table is computed from jl_gc_sizeclasses via the formula:
-// [searchsortedfirst(TABLE, i) for i = 0:16:table[end]]
-static const uint8_t szclass_table[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 20, 21, 21, 22, 22, 23, 23, 23, 24, 24, 24, 25, 25, 25, 26, 26, 27, 27, 27, 28, 28, 28, 29, 29, 29, 29, 30, 30, 30, 30, 30, 31, 31, 31, 31, 31, 32, 32, 32, 32, 32, 32, 32, 33, 33, 33, 33, 33, 34, 34, 34, 34, 34, 35, 35, 35, 35, 35, 36, 36, 36, 36, 36, 36, 36, 37, 37, 37, 37, 37, 37, 37, 37, 38, 38, 38, 38, 38, 38, 38, 38, 38, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40};
+// the following table is computed as:
+// [searchsortedfirst(jl_gc_sizeclasses, i) - 1 for i = 0:16:jl_gc_sizeclasses[end]]
+static const uint8_t szclass_table[] = {0, 1, 3, 5, 7, 9, 11, 13, 15, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 28, 29, 29, 30, 30, 31, 31, 31, 32, 32, 32, 33, 33, 33, 34, 34, 35, 35, 35, 36, 36, 36, 37, 37, 37, 37, 38, 38, 38, 38, 38, 39, 39, 39, 39, 39, 40, 40, 40, 40, 40, 40, 40, 41, 41, 41, 41, 41, 42, 42, 42, 42, 42, 43, 43, 43, 43, 43, 44, 44, 44, 44, 44, 44, 44, 45, 45, 45, 45, 45, 45, 45, 45, 46, 46, 46, 46, 46, 46, 46, 46, 46, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48};
 static_assert(sizeof(szclass_table) == 128, "");
 
 STATIC_INLINE uint8_t JL_CONST_FUNC jl_gc_szclass(unsigned sz)
 {
     assert(sz <= 2032);
-    uint8_t klass = szclass_table[(sz + 15) / 16];
 #ifdef _P64
     if (sz <= 8)
         return 0;
@@ -315,9 +317,25 @@ STATIC_INLINE uint8_t JL_CONST_FUNC jl_gc_szclass(unsigned sz)
         return (sz >= 8 ? 2 : (sz >= 4 ? 1 : 0));
     const int N = 2;
 #endif
+    uint8_t klass = szclass_table[(sz + 15) / 16];
     return klass + N;
 }
 
+STATIC_INLINE uint8_t JL_CONST_FUNC jl_gc_szclass_align8(unsigned sz)
+{
+    if (sz >= 16 && sz <= 152) {
+#ifdef _P64
+        const int N = 0;
+#elif MAX_ALIGN == 8
+        const int N = 1;
+#else
+        const int N = 2;
+#endif
+        return (sz + 7)/8 - 1 + N;
+    }
+    return jl_gc_szclass(sz);
+}
+
 #define JL_SMALL_BYTE_ALIGNMENT 16
 #define JL_CACHE_BYTE_ALIGNMENT 64
 // JL_HEAP_ALIGNMENT is the maximum alignment that the GC can provide
diff --git a/src/julia_threads.h b/src/julia_threads.h
index d0d70f88c79db..f10c9f538915d 100644
--- a/src/julia_threads.h
+++ b/src/julia_threads.h
@@ -141,11 +141,11 @@ typedef struct {
 
     // variables for allocating objects from pools
 #ifdef _P64
-#  define JL_GC_N_POOLS 41
+#  define JL_GC_N_POOLS 49
 #elif MAX_ALIGN == 8
-#  define JL_GC_N_POOLS 42
+#  define JL_GC_N_POOLS 50
 #else
-#  define JL_GC_N_POOLS 43
+#  define JL_GC_N_POOLS 51
 #endif
     jl_gc_pool_t norm_pools[JL_GC_N_POOLS];