[SectionMemoryManager] Make better use of virtual memory

Summary: On Windows, the allocation granularity can be significantly
larger than a page (64K), so with many small objects, just clearing
the FreeMem list rapidly leaks quite a bit of virtual memory space
(if not rss). Fix that by only removing those parts of the FreeMem
blocks that overlap pages for which we are applying memory permissions,
rather than dropping the FreeMem blocks entirely.

Reviewers: lhames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D15202

llvm-svn: 255760

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Support/Unix/Memory.inc b/llvm/lib/Support/Unix/Memory.inc
index 7bffdf38773..d70319168b8 100644
--- a/llvm/lib/Support/Unix/Memory.inc
+++ b/llvm/lib/Support/Unix/Memory.inc
@@ -152,6 +152,7 @@ Memory::releaseMappedMemory(MemoryBlock &M) {
 
 std::error_code
 Memory::protectMappedMemory(const MemoryBlock &M, unsigned Flags) {
+  static const size_t PageSize = Process::getPageSize();
   if (M.Address == nullptr || M.Size == 0)
     return std::error_code();
 
@@ -160,7 +161,7 @@ Memory::protectMappedMemory(const MemoryBlock &M, unsigned Flags) {
 
   int Protect = getPosixProtectionFlags(Flags);
 
-  int Result = ::mprotect(M.Address, M.Size, Protect);
+  int Result = ::mprotect((void*)((uintptr_t)M.Address & ~(PageSize-1)), PageSize*((M.Size+PageSize-1)/PageSize), Protect);
   if (Result != 0)
     return std::error_code(errno, std::generic_category());
 
@@ -180,7 +181,7 @@ Memory::AllocateRWX(size_t NumBytes, const MemoryBlock* NearBlock,
                     std::string *ErrMsg) {
   if (NumBytes == 0) return MemoryBlock();
 
-  size_t PageSize = Process::getPageSize();
+  static const size_t PageSize = Process::getPageSize();
   size_t NumPages = (NumBytes+PageSize-1)/PageSize;
 
   int fd = -1;