diff --git a/compiler-rt/lib/dfsan/dfsan.cpp b/compiler-rt/lib/dfsan/dfsan.cpp
--- a/compiler-rt/lib/dfsan/dfsan.cpp
+++ b/compiler-rt/lib/dfsan/dfsan.cpp
@@ -274,9 +274,9 @@
   return label;
 }
 
-extern "C" SANITIZER_INTERFACE_ATTRIBUTE
-void __dfsan_set_label(dfsan_label label, void *addr, uptr size) {
-  for (dfsan_label *labelp = shadow_for(addr); size != 0; --size, ++labelp) {
+static void __dfsan_set_label_at_shadow_space(dfsan_label label,
+                                              dfsan_label *labelp, uptr size) {
+  for (; size != 0; --size, ++labelp) {
     // Don't write the label if it is already the value we need it to be.
     // In a program where most addresses are not labeled, it is common that
     // a page of shadow memory is entirely zeroed.  The Linux copy-on-write
@@ -292,6 +292,37 @@
   }
 }
 
+extern "C" SANITIZER_INTERFACE_ATTRIBUTE void __dfsan_set_label(
+    dfsan_label label, void *addr, uptr size) {
+  const uptr beg_shadow_addr = (uptr)__dfsan::shadow_for(addr);
+
+  if (0 != label) {
+    __dfsan_set_label_at_shadow_space(label, (dfsan_label *)beg_shadow_addr,
+                                      size);
+    return;
+  }
+
+  // If label is 0, releases the pages within the shadow address range, and sets
+  // the shadow addresses not on the pages to be 0.
+  const void *end_addr = (void *)((uptr)addr + size);
+  const uptr end_shadow_addr = (uptr)__dfsan::shadow_for(end_addr);
+  const uptr page_size = GetPageSizeCached();
+  const uptr beg_aligned = RoundUpTo(beg_shadow_addr, page_size);
+  const uptr end_aligned = RoundDownTo(end_shadow_addr, page_size);
+
+  // When the entire shadow address range is on one page, it is not possible to
+  // release the page.
+  if (beg_aligned >= end_aligned)
+    return __dfsan_set_label_at_shadow_space(
+        label, (dfsan_label *)beg_shadow_addr, size);
+
+  __dfsan_set_label_at_shadow_space(label, (dfsan_label *)beg_shadow_addr,
+                                    beg_aligned - beg_shadow_addr);
+  ReleaseMemoryPagesToOS(beg_aligned, end_aligned);
+  __dfsan_set_label_at_shadow_space(label, (dfsan_label *)end_aligned,
+                                    end_shadow_addr - end_aligned);
+}
+
 SANITIZER_INTERFACE_ATTRIBUTE
 void dfsan_set_label(dfsan_label label, void *addr, uptr size) {
   __dfsan_set_label(label, addr, size);
diff --git a/compiler-rt/lib/dfsan/dfsan_interceptors.cpp b/compiler-rt/lib/dfsan/dfsan_interceptors.cpp
--- a/compiler-rt/lib/dfsan/dfsan_interceptors.cpp
+++ b/compiler-rt/lib/dfsan/dfsan_interceptors.cpp
@@ -20,19 +20,7 @@
 
 using namespace __sanitizer;
 
-namespace {
-
-bool interceptors_initialized;
-
-void ReleaseShadowMemoryPagesToOS(void *addr, SIZE_T length) {
-  uptr beg_shadow_addr = (uptr)__dfsan::shadow_for(addr);
-  void *end_addr =
-      (void *)((uptr)addr + RoundUpTo(length, GetPageSizeCached()));
-  uptr end_shadow_addr = (uptr)__dfsan::shadow_for(end_addr);
-  ReleaseMemoryPagesToOS(beg_shadow_addr, end_shadow_addr);
-}
-
-}  // namespace
+static bool interceptors_initialized;
 
 INTERCEPTOR(void *, mmap, void *addr, SIZE_T length, int prot, int flags,
             int fd, OFF_T offset) {
@@ -46,7 +34,7 @@
     res = REAL(mmap)(addr, length, prot, flags, fd, offset);
 
   if (res != (void *)-1)
-    ReleaseShadowMemoryPagesToOS(res, length);
+    dfsan_set_label(0, res, RoundUpTo(length, GetPageSizeCached()));
   return res;
 }
 
@@ -54,15 +42,14 @@
             int fd, OFF64_T offset) {
   void *res = REAL(mmap64)(addr, length, prot, flags, fd, offset);
   if (res != (void *)-1)
-    ReleaseShadowMemoryPagesToOS(res, length);
+    dfsan_set_label(0, res, RoundUpTo(length, GetPageSizeCached()));
   return res;
 }
 
 INTERCEPTOR(int, munmap, void *addr, SIZE_T length) {
   int res = REAL(munmap)(addr, length);
-  if (res != -1) {
-    ReleaseShadowMemoryPagesToOS(addr, length);
-  }
+  if (res != -1)
+    dfsan_set_label(0, addr, RoundUpTo(length, GetPageSizeCached()));
   return res;
 }