Release memory to OS only when the requested range covers the entire page

Summary:
The current code was sometimes attempting to release huge chunks of
memory due to undesired RoundUp/RoundDown interaction when the requested
range is fully contained within one memory page.

Reviewers: eugenis

Subscribers: kubabrecka, llvm-commits

Patch by Aleksey Shlyapnikov.

Differential Revision: https://reviews.llvm.org/D27228

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@288271 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 2 deletions

diff --git a/lib/sanitizer_common/sanitizer_posix_libcdep.cc b/lib/sanitizer_common/sanitizer_posix_libcdep.cc
index 71eda4e80..dd62140b5 100644
--- a/lib/sanitizer_common/sanitizer_posix_libcdep.cc
+++ b/lib/sanitizer_common/sanitizer_posix_libcdep.cc
@@ -56,8 +56,12 @@ uptr GetThreadSelf() {
   return (uptr)pthread_self();
 }
 
-void ReleaseMemoryToOS(uptr addr, uptr size) {
-  madvise((void*)addr, size, MADV_DONTNEED);
+void ReleaseMemoryPagesToOS(uptr beg, uptr end) {
+  uptr page_size = GetPageSizeCached();
+  uptr beg_aligned = RoundUpTo(beg, page_size);
+  uptr end_aligned = RoundDownTo(end, page_size);
+  if (beg_aligned < end_aligned)
+    madvise((void*)beg_aligned, end_aligned - beg_aligned, MADV_DONTNEED);
 }
 
 void NoHugePagesInRegion(uptr addr, uptr size) {