diff --git a/include/mimalloc/internal.h b/include/mimalloc/internal.h
index 7af1e6e1..92fbca27 100644
--- a/include/mimalloc/internal.h
+++ b/include/mimalloc/internal.h
@@ -8,7 +8,6 @@ terms of the MIT license. A copy of the license can be found in the file
 #ifndef MIMALLOC_INTERNAL_H
 #define MIMALLOC_INTERNAL_H
 
-
 // --------------------------------------------------------------------------
 // This file contains the internal API's of mimalloc and various utility
 // functions and macros.
@@ -17,50 +16,88 @@ terms of the MIT license. A copy of the license can be found in the file
 #include "types.h"
 #include "track.h"
 
+
+// --------------------------------------------------------------------------
+// Compiler defines
+// --------------------------------------------------------------------------
+
 #if (MI_DEBUG>0)
 #define mi_trace_message(...)  _mi_trace_message(__VA_ARGS__)
 #else
 #define mi_trace_message(...)
 #endif
 
-#define MI_CACHE_LINE          64
+#define mi_decl_cache_align     mi_decl_align(64)
+
 #if defined(_MSC_VER)
 #pragma warning(disable:4127)   // suppress constant conditional warning (due to MI_SECURE paths)
 #pragma warning(disable:26812)  // unscoped enum warning
 #define mi_decl_noinline        __declspec(noinline)
 #define mi_decl_thread          __declspec(thread)
-#define mi_decl_cache_align     __declspec(align(MI_CACHE_LINE))
+#define mi_decl_align(a)        __declspec(align(a))
+#define mi_decl_noreturn        __declspec(noreturn)
 #define mi_decl_weak
 #define mi_decl_hidden
+#define mi_decl_cold
 #elif (defined(__GNUC__) && (__GNUC__ >= 3)) || defined(__clang__) // includes clang and icc
 #define mi_decl_noinline        __attribute__((noinline))
 #define mi_decl_thread          __thread
-#define mi_decl_cache_align     __attribute__((aligned(MI_CACHE_LINE)))
+#define mi_decl_align(a)        __attribute__((aligned(a)))
+#define mi_decl_noreturn        __attribute__((noreturn))
 #define mi_decl_weak            __attribute__((weak))
 #define mi_decl_hidden          __attribute__((visibility("hidden")))
+#if (__GNUC__ >= 4) || defined(__clang__)
+#define mi_decl_cold            __attribute__((cold))
+#else
+#define mi_decl_cold
+#endif
 #elif __cplusplus >= 201103L    // c++11
 #define mi_decl_noinline
 #define mi_decl_thread          thread_local
-#define mi_decl_cache_align     alignas(MI_CACHE_LINE)
+#define mi_decl_align(a)        alignas(a)
+#define mi_decl_noreturn        [[noreturn]]
 #define mi_decl_weak
 #define mi_decl_hidden
+#define mi_decl_cold
 #else
 #define mi_decl_noinline
 #define mi_decl_thread          __thread        // hope for the best :-)
-#define mi_decl_cache_align
+#define mi_decl_align(a)
+#define mi_decl_noreturn        
 #define mi_decl_weak
 #define mi_decl_hidden
+#define mi_decl_cold
+#endif
+
+#if defined(__GNUC__) || defined(__clang__)
+#define mi_unlikely(x)     (__builtin_expect(!!(x),false))
+#define mi_likely(x)       (__builtin_expect(!!(x),true))
+#elif (defined(__cplusplus) && (__cplusplus >= 202002L)) || (defined(_MSVC_LANG) && _MSVC_LANG >= 202002L)
+#define mi_unlikely(x)     (x) [[unlikely]]
+#define mi_likely(x)       (x) [[likely]]
+#else
+#define mi_unlikely(x)     (x)
+#define mi_likely(x)       (x)
+#endif
+
+#ifndef __has_builtin
+#define __has_builtin(x)    0
+#endif
+
+#if defined(__cplusplus)
+#define mi_decl_externc     extern "C"
+#else
+#define mi_decl_externc
 #endif
 
 #if defined(__EMSCRIPTEN__) && !defined(__wasi__)
 #define __wasi__
 #endif
 
-#if defined(__cplusplus)
-#define mi_decl_externc       extern "C"
-#else
-#define mi_decl_externc
-#endif
+
+// --------------------------------------------------------------------------
+// Internal functions
+// --------------------------------------------------------------------------
 
 // "libc.c"
 #include    <stdarg.h>
@@ -126,13 +163,13 @@ bool        _mi_os_has_overcommit(void);
 bool        _mi_os_has_virtual_reserve(void);
 
 bool        _mi_os_reset(void* addr, size_t size);
-bool        _mi_os_commit(void* p, size_t size, bool* is_zero);
-bool        _mi_os_commit_ex(void* addr, size_t size, bool* is_zero, size_t stat_size);
 bool        _mi_os_decommit(void* addr, size_t size);
-bool        _mi_os_protect(void* addr, size_t size);
 bool        _mi_os_unprotect(void* addr, size_t size);
 bool        _mi_os_purge(void* p, size_t size);
 bool        _mi_os_purge_ex(void* p, size_t size, bool allow_reset, size_t stat_size);
+mi_decl_nodiscard bool _mi_os_commit(void* p, size_t size, bool* is_zero);
+mi_decl_nodiscard bool _mi_os_commit_ex(void* addr, size_t size, bool* is_zero, size_t stat_size);
+bool        _mi_os_protect(void* addr, size_t size);
 
 void*       _mi_os_alloc_aligned(size_t size, size_t alignment, bool commit, bool allow_large, mi_memid_t* memid);
 void*       _mi_os_alloc_aligned_at_offset(size_t size, size_t alignment, size_t align_offset, bool commit, bool allow_large, mi_memid_t* memid);
@@ -258,26 +295,6 @@ bool        _mi_page_is_valid(mi_page_t* page);
 #endif
 
 
-// ------------------------------------------------------
-// Branches
-// ------------------------------------------------------
-
-#if defined(__GNUC__) || defined(__clang__)
-#define mi_unlikely(x)     (__builtin_expect(!!(x),false))
-#define mi_likely(x)       (__builtin_expect(!!(x),true))
-#elif (defined(__cplusplus) && (__cplusplus >= 202002L)) || (defined(_MSVC_LANG) && _MSVC_LANG >= 202002L)
-#define mi_unlikely(x)     (x) [[unlikely]]
-#define mi_likely(x)       (x) [[likely]]
-#else
-#define mi_unlikely(x)     (x)
-#define mi_likely(x)       (x)
-#endif
-
-#ifndef __has_builtin
-#define __has_builtin(x)  0
-#endif
-
-
 /* -----------------------------------------------------------
   Error codes passed to `_mi_fatal_error`
   All are recoverable but EFAULT is a serious error and aborts by default in secure mode.
@@ -302,6 +319,32 @@ bool        _mi_page_is_valid(mi_page_t* page);
 #endif
 
 
+// ------------------------------------------------------
+// Assertions
+// ------------------------------------------------------
+
+#if (MI_DEBUG)
+// use our own assertion to print without memory allocation
+mi_decl_noreturn mi_decl_cold void _mi_assert_fail(const char* assertion, const char* fname, unsigned int line, const char* func) mi_attr_noexcept;
+#define mi_assert(expr)     ((expr) ? (void)0 : _mi_assert_fail(#expr,__FILE__,__LINE__,__func__))
+#else
+#define mi_assert(x)
+#endif
+
+#if (MI_DEBUG>1)
+#define mi_assert_internal    mi_assert
+#else
+#define mi_assert_internal(x)
+#endif
+
+#if (MI_DEBUG>2)
+#define mi_assert_expensive   mi_assert
+#else
+#define mi_assert_expensive(x)
+#endif
+
+
+
 /* -----------------------------------------------------------
   Inlined definitions
 ----------------------------------------------------------- */
diff --git a/include/mimalloc/types.h b/include/mimalloc/types.h
index ce8b64d8..a15d9cba 100644
--- a/include/mimalloc/types.h
+++ b/include/mimalloc/types.h
@@ -632,7 +632,6 @@ struct mi_tld_s {
 };
 
 
-
 // ------------------------------------------------------
 // Debug
 // ------------------------------------------------------
@@ -647,26 +646,6 @@ struct mi_tld_s {
 #define MI_DEBUG_PADDING    (0xDE)
 #endif
 
-#if (MI_DEBUG)
-// use our own assertion to print without memory allocation
-void _mi_assert_fail(const char* assertion, const char* fname, unsigned int line, const char* func );
-#define mi_assert(expr)     ((expr) ? (void)0 : _mi_assert_fail(#expr,__FILE__,__LINE__,__func__))
-#else
-#define mi_assert(x)
-#endif
-
-#if (MI_DEBUG>1)
-#define mi_assert_internal    mi_assert
-#else
-#define mi_assert_internal(x)
-#endif
-
-#if (MI_DEBUG>2)
-#define mi_assert_expensive   mi_assert
-#else
-#define mi_assert_expensive(x)
-#endif
-
 
 // ------------------------------------------------------
 // Statistics
diff --git a/src/options.c b/src/options.c
index 4759e0b0..c2331ccb 100644
--- a/src/options.c
+++ b/src/options.c
@@ -525,7 +525,7 @@ void _mi_warning_message(const char* fmt, ...) {
 
 
 #if MI_DEBUG
-void _mi_assert_fail(const char* assertion, const char* fname, unsigned line, const char* func ) {
+mi_decl_noreturn mi_decl_cold void _mi_assert_fail(const char* assertion, const char* fname, unsigned line, const char* func ) mi_attr_noexcept {
   _mi_fprintf(NULL, NULL, "mimalloc: assertion failed: at \"%s\":%u, %s\n  assertion: \"%s\"\n", fname, line, (func==NULL?"":func), assertion);
   abort();
 }
diff --git a/src/os.c b/src/os.c
index ba0a6419..2af769a0 100644
--- a/src/os.c
+++ b/src/os.c
@@ -166,7 +166,7 @@ static void mi_os_prim_free(void* addr, size_t size, size_t commit_size) {
 void _mi_os_free_ex(void* addr, size_t size, bool still_committed, mi_memid_t memid) {
   if (mi_memkind_is_os(memid.memkind)) {
     size_t csize = memid.mem.os.size;
-    if (csize==0) { _mi_os_good_alloc_size(size); }
+    if (csize==0) { csize = _mi_os_good_alloc_size(size); }
     size_t commit_size = (still_committed ? csize : 0);
     void* base = addr;
     // different base? (due to alignment)
@@ -285,7 +285,10 @@ static void* mi_os_prim_alloc_aligned(size_t size, size_t alignment, bool commit
 
       // explicitly commit only the aligned part
       if (commit) {
-        _mi_os_commit(p, size, NULL);
+        if (!_mi_os_commit(p, size, NULL)) {
+          mi_os_prim_free(*base, over_size, 0);
+          return NULL;
+        }
       }
     }
     else  { // mmap can free inside an allocation
diff --git a/src/page.c b/src/page.c
index 2bbc2ed1..a5a10503 100644
--- a/src/page.c
+++ b/src/page.c
@@ -37,7 +37,7 @@ static inline mi_block_t* mi_page_block_at(const mi_page_t* page, void* page_sta
 }
 
 static void mi_page_init(mi_heap_t* heap, mi_page_t* page, size_t size, mi_tld_t* tld);
-static void mi_page_extend_free(mi_heap_t* heap, mi_page_t* page, mi_tld_t* tld);
+static bool mi_page_extend_free(mi_heap_t* heap, mi_page_t* page, mi_tld_t* tld);
 
 #if (MI_DEBUG>=3)
 static size_t mi_page_list_count(mi_page_t* page, mi_block_t* head) {
@@ -632,15 +632,14 @@ static mi_decl_noinline void mi_page_free_list_extend( mi_page_t* const page, co
 // Note: we also experimented with "bump" allocation on the first
 // allocations but this did not speed up any benchmark (due to an
 // extra test in malloc? or cache effects?)
-static void mi_page_extend_free(mi_heap_t* heap, mi_page_t* page, mi_tld_t* tld) {
-  MI_UNUSED(tld);
+static bool mi_page_extend_free(mi_heap_t* heap, mi_page_t* page, mi_tld_t* tld) {
   mi_assert_expensive(mi_page_is_valid_init(page));
   #if (MI_SECURE<=2)
   mi_assert(page->free == NULL);
   mi_assert(page->local_free == NULL);
-  if (page->free != NULL) return;
+  if (page->free != NULL) return true;
   #endif
-  if (page->capacity >= page->reserved) return;
+  if (page->capacity >= page->reserved) return true;
 
   mi_stat_counter_increase(tld->stats.pages_extended, 1);
 
@@ -673,6 +672,7 @@ static void mi_page_extend_free(mi_heap_t* heap, mi_page_t* page, mi_tld_t* tld)
   page->capacity += (uint16_t)extend;
   mi_stat_increase(tld->stats.page_committed, extend * bsize);
   mi_assert_expensive(mi_page_is_valid_init(page));
+  return true;
 }
 
 // Initialize a fresh page
@@ -727,8 +727,10 @@ static void mi_page_init(mi_heap_t* heap, mi_page_t* page, size_t block_size, mi
   mi_assert_expensive(mi_page_is_valid_init(page));
 
   // initialize an initial free list
-  mi_page_extend_free(heap,page,tld);
-  mi_assert(mi_page_immediate_available(page));
+  if (mi_page_extend_free(heap,page,tld)) {
+    mi_assert(mi_page_immediate_available(page));
+  }
+  return;
 }
 
 
@@ -820,9 +822,14 @@ static mi_page_t* mi_page_queue_find_free_ex(mi_heap_t* heap, mi_page_queue_t* p
   if (page_candidate != NULL) {
     page = page_candidate;
   }
-  if (page != NULL && !mi_page_immediate_available(page)) {
-    mi_assert_internal(mi_page_is_expandable(page));
-    mi_page_extend_free(heap, page, heap->tld);
+  if (page != NULL) {
+    if (!mi_page_immediate_available(page)) {
+      mi_assert_internal(mi_page_is_expandable(page));
+      if (!mi_page_extend_free(heap, page, heap->tld)) {
+        page = NULL; // failed to extend
+      }
+    }
+    mi_assert_internal(page == NULL || mi_page_immediate_available(page));
   }
 
   if (page == NULL) {