Fix implementation of GCToOSInterface::VirtualCommit to ditch the pages (#4907)

The GC depends on the pages to be zeroed out when they are mapped in again

1 files changed, 6 insertions, 1 deletions

diff --git a/src/Native/Runtime/unix/PalRedhawkUnix.cpp b/src/Native/Runtime/unix/PalRedhawkUnix.cpp
index 0357d6058..0c0c035e1 100644
--- a/src/Native/Runtime/unix/PalRedhawkUnix.cpp
+++ b/src/Native/Runtime/unix/PalRedhawkUnix.cpp
@@ -1537,7 +1537,12 @@ bool GCToOSInterface::VirtualCommit(void* address, size_t size)
 //  true if it has succeeded, false if it has failed
 bool GCToOSInterface::VirtualDecommit(void* address, size_t size)
 {
-    return mprotect(address, size, PROT_NONE) == 0;
+    // TODO: This can fail, however the GC does not handle the failure gracefully
+    // Explicitly calling mmap instead of mprotect here makes it
+    // that much more clear to the operating system that we no
+    // longer need these pages. Also, GC depends on re-commited pages to
+    // be zeroed-out.
+    return mmap(address, size, PROT_NONE, MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0) != NULL;
 }
 
 // Reset virtual memory range. Indicates that data in the memory range specified by address and size is no