diff --git a/include/mimalloc/prim.h b/include/mimalloc/prim.h
index 4d813b7f..9561335a 100644
--- a/include/mimalloc/prim.h
+++ b/include/mimalloc/prim.h
@@ -26,7 +26,7 @@ typedef struct mi_os_mem_config_s {
   size_t  large_page_size;      // 0 if not supported, usually 2MiB (4MiB on Windows)
   size_t  alloc_granularity;    // smallest allocation size (usually 4KiB, on Windows 64KiB)
   bool    has_overcommit;       // can we reserve more memory than can be actually committed?
-  bool    must_free_whole;      // must allocated blocks be freed as a whole (false for mmap, true for VirtualAlloc)
+  bool    has_partial_free;     // can allocated blocks be freed partially? (true for mmap, false for VirtualAlloc)
   bool    has_virtual_reserve;  // supports virtual address space reservation? (if true we can reserve virtual address space without using commit or physical memory)
 } mi_os_mem_config_t;
 
diff --git a/src/os.c b/src/os.c
index 09ae367d..88e7fcb3 100644
--- a/src/os.c
+++ b/src/os.c
@@ -11,9 +11,7 @@ terms of the MIT license. A copy of the license can be found in the file
 
 
 /* -----------------------------------------------------------
-  Initialization.
-  On windows initializes support for aligned allocation and
-  large OS pages (if MIMALLOC_LARGE_OS_PAGES is true).
+  Initialization. 
 ----------------------------------------------------------- */
 
 static mi_os_mem_config_t mi_os_mem_config = {
@@ -21,7 +19,7 @@ static mi_os_mem_config_t mi_os_mem_config = {
   0,      // large page size (usually 2MiB)
   4096,   // allocation granularity
   true,   // has overcommit?  (if true we use MAP_NORESERVE on mmap systems)
-  false,  // must free whole? (on mmap systems we can free anywhere in a mapped range, but on Windows we must free the entire span)
+  false,  // can we partially free allocated blocks? (on mmap systems we can free anywhere in a mapped range, but on Windows we must free the entire span)
   true    // has virtual reserve? (if true we can reserve virtual address space without using commit or physical memory)
 };
 
@@ -254,7 +252,7 @@ static void* mi_os_prim_alloc_aligned(size_t size, size_t alignment, bool commit
     if (size >= (SIZE_MAX - alignment)) return NULL; // overflow
     const size_t over_size = size + alignment;
 
-    if (mi_os_mem_config.must_free_whole) {  // win32 virtualAlloc cannot free parts of an allocate block
+    if (!mi_os_mem_config.has_partial_free) {  // win32 virtualAlloc cannot free parts of an allocated block
       // over-allocate uncommitted (virtual) memory
       p = mi_os_prim_alloc(over_size, 1 /*alignment*/, false /* commit? */, false /* allow_large */, is_large, is_zero, stats);
       if (p == NULL) return NULL;
@@ -275,7 +273,7 @@ static void* mi_os_prim_alloc_aligned(size_t size, size_t alignment, bool commit
       p = mi_os_prim_alloc(over_size, 1, commit, false, is_large, is_zero, stats);
       if (p == NULL) return NULL;
 
-      // and selectively unmap parts around the over-allocated area. (noop on sbrk)
+      // and selectively unmap parts around the over-allocated area. 
       void* aligned_p = mi_align_up_ptr(p, alignment);
       size_t pre_size = (uint8_t*)aligned_p - (uint8_t*)p;
       size_t mid_size = _mi_align_up(size, _mi_os_page_size());
@@ -283,7 +281,7 @@ static void* mi_os_prim_alloc_aligned(size_t size, size_t alignment, bool commit
       mi_assert_internal(pre_size < over_size&& post_size < over_size&& mid_size >= size);
       if (pre_size > 0)  { mi_os_prim_free(p, pre_size, commit, stats); }
       if (post_size > 0) { mi_os_prim_free((uint8_t*)aligned_p + mid_size, post_size, commit, stats); }
-      // we can return the aligned pointer on `mmap` (and sbrk) systems
+      // we can return the aligned pointer on `mmap` systems
       p = aligned_p;
       *base = aligned_p; // since we freed the pre part, `*base == p`.
     }
diff --git a/src/prim/emscripten/prim.c b/src/prim/emscripten/prim.c
index 1f60a1bb..f3797c9e 100644
--- a/src/prim/emscripten/prim.c
+++ b/src/prim/emscripten/prim.c
@@ -51,7 +51,7 @@ void _mi_prim_mem_init( mi_os_mem_config_t* config) {
   config->page_size = 64*MI_KiB; // WebAssembly has a fixed page size: 64KiB
   config->alloc_granularity = 16;
   config->has_overcommit = false;
-  config->must_free_whole = true;
+  config->has_partial_free = false;
   config->has_virtual_reserve = false;
 }
 
diff --git a/src/prim/unix/prim.c b/src/prim/unix/prim.c
index a7812cb6..8093fbdd 100644
--- a/src/prim/unix/prim.c
+++ b/src/prim/unix/prim.c
@@ -144,7 +144,7 @@ void _mi_prim_mem_init( mi_os_mem_config_t* config )
   }
   config->large_page_size = 2*MI_MiB; // TODO: can we query the OS for this?
   config->has_overcommit = unix_detect_overcommit();
-  config->must_free_whole = false;    // mmap can free in parts
+  config->has_partial_free = true;    // mmap can free in parts
   config->has_virtual_reserve = true; // todo: check if this true for NetBSD?  (for anonymous mmap with PROT_NONE)
 
   // disable transparent huge pages for this process?
diff --git a/src/prim/wasi/prim.c b/src/prim/wasi/prim.c
index f74acd2a..e95f67f5 100644
--- a/src/prim/wasi/prim.c
+++ b/src/prim/wasi/prim.c
@@ -23,7 +23,7 @@ void _mi_prim_mem_init( mi_os_mem_config_t* config ) {
   config->page_size = 64*MI_KiB; // WebAssembly has a fixed page size: 64KiB
   config->alloc_granularity = 16;
   config->has_overcommit = false;  
-  config->must_free_whole = true;
+  config->has_partial_free = false;
   config->has_virtual_reserve = false;
 }
 
diff --git a/src/prim/windows/prim.c b/src/prim/windows/prim.c
index 2dd7c602..05aab43a 100644
--- a/src/prim/windows/prim.c
+++ b/src/prim/windows/prim.c
@@ -112,7 +112,7 @@ static bool win_enable_large_os_pages(size_t* large_page_size)
 void _mi_prim_mem_init( mi_os_mem_config_t* config )
 {
   config->has_overcommit = false;
-  config->must_free_whole = true;
+  config->has_partial_free = false;
   config->has_virtual_reserve = true;
   // get the page size
   SYSTEM_INFO si;