Comment 75 for bug 1751460

Here's a debug patch:

diff --git a/Source/bmalloc/bmalloc/VMAllocate.h b/Source/bmalloc/bmalloc/VMAllocate.h
index 713e9c9fbb6..5c9c8553b1a 100644
--- a/Source/bmalloc/bmalloc/VMAllocate.h
+++ b/Source/bmalloc/bmalloc/VMAllocate.h
@@ -35,6 +35,9 @@
 #include <sys/mman.h>
 #include <unistd.h>

+#include <cstdio>
+#include <errno.h>
+
 #if BOS(DARWIN)
 #include <mach/vm_page_size.h>
 #include <mach/vm_statistics.h>
@@ -123,7 +126,10 @@ inline void* tryVMAllocate(size_t vmSize)
     vmValidate(vmSize);
     void* result = mmap(0, vmSize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON | BMALLOC_NORESERVE, BMALLOC_VM_TAG, 0);
     if (result == MAP_FAILED)
+{
+fprintf(stderr, "%s: mmap failed: vmSize=%zu errno=%d (%s)", __FUNCTION__, vmSize, errno, strerror(errno));
         return nullptr;
+}
     return result;
 }