[Memory] Add basic support for large/huge memory pages

This patch introduces Memory::MF_HUGE_HINT which indicates that allocateMappedMemory() shall return a pointer to a large memory page.
However the flag is a hint because we're not guaranteed in any way that we will get back a large memory page. There are several restrictions:

- Large/huge memory pages aren't enabled by default on modern OSes (Windows 10 and Linux at least), and should be manually enabled/reserved.
- Once enabled, it should be kept in mind that large pages are physical only, they can't be swapped.
- Memory fragmentation can affect the availability of large pages, especially after running the OS for a long time and/or running along many other applications.

Memory::allocateMappedMemory() will fallback to 4KB pages if it can't allocate 2MB large pages (if Memory::MF_HUGE_HINT is provided)

Currently, Memory::MF_HUGE_HINT only works on Windows. The hint will be ignored on Linux, 4KB pages will always be returned.

Differential Revision: https://reviews.llvm.org/D58718

llvm-svn: 355065

1 files changed, 16 insertions, 0 deletions

diff --git a/llvm/unittests/Support/MemoryTest.cpp b/llvm/unittests/Support/MemoryTest.cpp
index 473a0da97c8..33cc3edb815 100644
--- a/llvm/unittests/Support/MemoryTest.cpp
+++ b/llvm/unittests/Support/MemoryTest.cpp
@@ -105,6 +105,22 @@ TEST_P(MappedMemoryTest, AllocAndRelease) {
   EXPECT_FALSE(Memory::releaseMappedMemory(M1));
 }
 
+TEST_P(MappedMemoryTest, AllocAndReleaseHuge) {
+  CHECK_UNSUPPORTED();
+  std::error_code EC;
+  MemoryBlock M1 = Memory::allocateMappedMemory(
+      sizeof(int), nullptr, Flags | Memory::MF_HUGE_HINT, EC);
+  EXPECT_EQ(std::error_code(), EC);
+
+  // Test large/huge memory pages. In the worst case, 4kb pages should be
+  // returned, if large pages aren't available.
+
+  EXPECT_NE((void *)nullptr, M1.base());
+  EXPECT_LE(sizeof(int), M1.size());
+
+  EXPECT_FALSE(Memory::releaseMappedMemory(M1));
+}
+
 TEST_P(MappedMemoryTest, MultipleAllocAndRelease) {
   CHECK_UNSUPPORTED();
   std::error_code EC;