[XRay][compiler-rt] Remove MAP_NORESERVE from XRay allocations

Summary:
This reverses an earlier decision to allow seg-faulting from the
XRay-allocated memory if it turns out that the system cannot provide
physical memory backing that cannot be swapped in/out on Linux.

This addresses http://llvm.org/PR38588.

Reviewers: eizan

Reviewed By: eizan

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D50831

llvm-svn: 339869

2 files changed, 3 insertions, 27 deletions

diff --git a/compiler-rt/lib/xray/xray_allocator.h b/compiler-rt/lib/xray/xray_allocator.h
index 8244815284a..27026211895 100644
--- a/compiler-rt/lib/xray/xray_allocator.h
+++ b/compiler-rt/lib/xray/xray_allocator.h
@@ -21,14 +21,9 @@
 #include "sanitizer_common/sanitizer_mutex.h"
 #include "sanitizer_common/sanitizer_posix.h"
 #include "xray_utils.h"
-#include <sys/mman.h>
 #include <cstddef>
 #include <cstdint>
-
-#ifndef MAP_NORESERVE
-// no-op on NetBSD (at least), unsupported flag on FreeBSD basically because unneeded
-#define MAP_NORESERVE 0
-#endif
+#include <sys/mman.h>
 
 namespace __xray {
 
@@ -69,7 +64,7 @@ private:
     if (UNLIKELY(BackingStore == nullptr)) {
       BackingStore = reinterpret_cast<void *>(
           internal_mmap(NULL, MaxMemory, PROT_READ | PROT_WRITE,
-                        MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, 0, 0));
+                        MAP_PRIVATE | MAP_ANONYMOUS, 0, 0));
       if (BackingStore == MAP_FAILED) {
         BackingStore = nullptr;
         if (Verbosity())
diff --git a/compiler-rt/lib/xray/xray_buffer_queue.cc b/compiler-rt/lib/xray/xray_buffer_queue.cc
index 3ce72890078..5bdd9148d54 100644
--- a/compiler-rt/lib/xray/xray_buffer_queue.cc
+++ b/compiler-rt/lib/xray/xray_buffer_queue.cc
@@ -19,33 +19,14 @@
 #include <memory>
 #include <sys/mman.h>
 
-#ifndef MAP_NORESERVE
-// no-op on NetBSD (at least), unsupported flag on FreeBSD
-#define MAP_NORESERVE 0
-#endif
-
 using namespace __xray;
 using namespace __sanitizer;
 
 template <class T> static T *allocRaw(size_t N) {
   // TODO: Report errors?
-  // We use MAP_NORESERVE on platforms where it's supported to ensure that the
-  // pages we're allocating for XRay never end up in pages that can be swapped
-  // in/out. We're doing this because for FDR mode, we want to ensure that
-  // writes to the buffers stay resident in memory to prevent XRay itself from
-  // causing swapping/thrashing.
-  //
-  // In the case when XRay pages cannot be swapped in/out or there's not enough
-  // RAM to back these pages, we're willing to cause a segmentation fault
-  // instead of introducing latency in the measurement. We assume here that
-  // there are enough pages that are swappable in/out outside of the buffers
-  // being used by FDR mode (which are bounded and configurable anyway) to allow
-  // us to keep using always-resident memory.
-  //
-  // TODO: Make this configurable?
   void *A = reinterpret_cast<void *>(
       internal_mmap(NULL, N * sizeof(T), PROT_WRITE | PROT_READ,
-                    MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE, -1, 0));
+                    MAP_ANONYMOUS | MAP_PRIVATE, -1, 0));
   return (A == MAP_FAILED) ? nullptr : reinterpret_cast<T *>(A);
 }