diff --git a/src/gc-common.c b/src/gc-common.c
index ee461b576ea9e7..a299b8aec21502 100644
--- a/src/gc-common.c
+++ b/src/gc-common.c
@@ -6,9 +6,6 @@
 #include "julia_gcext.h"
 #include "julia_assert.h"
 #include "threading.h"
-#ifdef __GLIBC__
-#include <malloc.h> // for malloc_trim
-#endif
 
 #ifdef __cplusplus
 extern "C" {
@@ -115,6 +112,21 @@ JL_DLLEXPORT void jl_gc_set_cb_notify_gc_pressure(jl_gc_cb_notify_gc_pressure_t
         jl_gc_deregister_callback(&gc_cblist_notify_gc_pressure, (jl_gc_cb_func_t)cb);
 }
 
+// =========================================================================== //
+// malloc wrappers, aligned allocation
+// =========================================================================== //
+
+size_t memory_block_usable_size(void *p) JL_NOTSAFEPOINT
+{
+#if defined(_OS_WINDOWS_)
+    return _aligned_msize(p, JL_CACHE_BYTE_ALIGNMENT, 0);
+#elif defined(_OS_DARWIN_)
+    return malloc_size(p);
+#else
+    return malloc_usable_size(p);
+#endif
+}
+
 // =========================================================================== //
 // Finalization
 // =========================================================================== //
diff --git a/src/gc-common.h b/src/gc-common.h
index 4d53830442a7dc..d721cb75ffde12 100644
--- a/src/gc-common.h
+++ b/src/gc-common.h
@@ -12,6 +12,12 @@
 #endif
 #endif
 
+#if defined(_OS_DARWIN_)
+#include <malloc/malloc.h>
+#else
+#include <malloc.h> // for malloc_trim
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/src/gc-stock.c b/src/gc-stock.c
index 1fc2087da6503f..8a58474052e845 100644
--- a/src/gc-stock.c
+++ b/src/gc-stock.c
@@ -9,9 +9,6 @@
 #include "julia_atomics.h"
 #include "julia_gcext.h"
 #include "julia_assert.h"
-#ifdef __GLIBC__
-#include <malloc.h> // for malloc_trim
-#endif
 
 #ifdef __cplusplus
 extern "C" {
@@ -579,11 +576,6 @@ void jl_gc_count_allocd(size_t sz) JL_NOTSAFEPOINT
     jl_batch_accum_heap_size(ptls, sz);
 }
 
-void jl_gc_count_freed(size_t sz) JL_NOTSAFEPOINT
-{
-    jl_batch_accum_free_size(jl_current_task->ptls, sz);
-}
-
 // Only safe to update the heap inside the GC
 static void combine_thread_gc_counts(jl_gc_num_t *dest, int update_heap) JL_NOTSAFEPOINT
 {
@@ -664,13 +656,15 @@ static void jl_gc_free_memory(jl_value_t *v, int isaligned) JL_NOTSAFEPOINT
     jl_genericmemory_t *m = (jl_genericmemory_t*)v;
     assert(jl_genericmemory_how(m) == 1 || jl_genericmemory_how(m) == 2);
     char *d = (char*)m->ptr;
+    size_t freed_bytes = memory_block_usable_size(d);
+    assert(freed_bytes != 0);
     if (isaligned)
         jl_free_aligned(d);
     else
         free(d);
     jl_atomic_store_relaxed(&gc_heap_stats.heap_size,
-        jl_atomic_load_relaxed(&gc_heap_stats.heap_size) - jl_genericmemory_nbytes(m));
-    gc_num.freed += jl_genericmemory_nbytes(m);
+        jl_atomic_load_relaxed(&gc_heap_stats.heap_size) - freed_bytes);
+    gc_num.freed += freed_bytes;
     gc_num.freecall++;
 }
 
@@ -3739,11 +3733,13 @@ JL_DLLEXPORT void *jl_gc_managed_malloc(size_t sz)
     if (b == NULL)
         jl_throw(jl_memory_exception);
 
+    size_t allocated_bytes = memory_block_usable_size(b);
+    assert(allocated_bytes >= allocsz);
     jl_atomic_store_relaxed(&ptls->gc_tls.gc_num.allocd,
-        jl_atomic_load_relaxed(&ptls->gc_tls.gc_num.allocd) + allocsz);
+        jl_atomic_load_relaxed(&ptls->gc_tls.gc_num.allocd) + allocated_bytes);
     jl_atomic_store_relaxed(&ptls->gc_tls.gc_num.malloc,
         jl_atomic_load_relaxed(&ptls->gc_tls.gc_num.malloc) + 1);
-    jl_batch_accum_heap_size(ptls, allocsz);
+    jl_batch_accum_heap_size(ptls, allocated_bytes);
 #ifdef _OS_WINDOWS_
     SetLastError(last_error);
 #endif
diff --git a/src/genericmemory.c b/src/genericmemory.c
index ea52fca66ba48b..3ad0776d272e95 100644
--- a/src/genericmemory.c
+++ b/src/genericmemory.c
@@ -165,7 +165,8 @@ JL_DLLEXPORT jl_genericmemory_t *jl_ptr_to_genericmemory(jl_value_t *mtype, void
     if (own_buffer) {
         int isaligned = 0;  // TODO: allow passing memalign'd buffers
         jl_gc_track_malloced_genericmemory(ct->ptls, m, isaligned);
-        jl_gc_count_allocd(nel*elsz);
+        size_t allocated_bytes = memory_block_usable_size(data);
+        jl_gc_count_allocd(allocated_bytes);
     }
     return m;
 }
@@ -208,8 +209,6 @@ JL_DLLEXPORT jl_value_t *jl_genericmemory_to_string(jl_genericmemory_t *m, size_
         JL_GC_PUSH1(&o);
         jl_value_t *str = jl_pchar_to_string((const char*)m->ptr, len);
         JL_GC_POP();
-        if (how == 1) // TODO: we might like to early-call jl_gc_free_memory here instead actually, but hopefully `m` will die soon
-            jl_gc_count_freed(mlength);
         return str;
     }
     // n.b. how == 0 is always pool-allocated, so the freed bytes are computed from the pool not the object
diff --git a/src/julia_internal.h b/src/julia_internal.h
index d4d1a3239785ca..a867c3fa7854c4 100644
--- a/src/julia_internal.h
+++ b/src/julia_internal.h
@@ -601,8 +601,8 @@ jl_svec_t *jl_perm_symsvec(size_t n, ...);
 
 void jl_gc_track_malloced_genericmemory(jl_ptls_t ptls, jl_genericmemory_t *m, int isaligned) JL_NOTSAFEPOINT;
 size_t jl_genericmemory_nbytes(jl_genericmemory_t *a) JL_NOTSAFEPOINT;
+size_t memory_block_usable_size(void *mem) JL_NOTSAFEPOINT;
 void jl_gc_count_allocd(size_t sz) JL_NOTSAFEPOINT;
-void jl_gc_count_freed(size_t sz) JL_NOTSAFEPOINT;
 void jl_gc_run_all_finalizers(jl_task_t *ct);
 void jl_release_task_stack(jl_ptls_t ptls, jl_task_t *task);
 void jl_gc_add_finalizer_(jl_ptls_t ptls, void *v, void *f) JL_NOTSAFEPOINT;