[Sanitizers] Set default allocator_release_to_os_interval_ms to 5 seconds

Summary:
With new release to OS approach (see D38245) it's reasonable to enable
it by default. Setting allocator_release_to_os_interval_ms to 5000 seems
to be a reasonable default (might be tuned later, based on the
feedback).

Also delaying the first release to OS in each bucket for at least
allocator_release_to_os_interval_ms after the first allocation to
prevent just allocated memory to be madvised back to OS and let short
lived processes to avoid release to OS overhead altogether.

Reviewers: cryptoad

Subscribers: kubamracek, llvm-commits, mehdi_amini

Differential Revision: https://reviews.llvm.org/D39318

llvm-svn: 316683

2 files changed, 13 insertions, 7 deletions

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary64.h b/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary64.h
index 8b7610b2cc2..b22f3aba9ca 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary64.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary64.h
@@ -669,10 +669,16 @@ class SizeClassAllocator64 {
 
     // Map more space for chunks, if necessary.
     if (new_space_end > region->mapped_user) {
-      if (!kUsingConstantSpaceBeg && kRandomShuffleChunks)
-        if (UNLIKELY(region->mapped_user == 0))
+      if (UNLIKELY(region->mapped_user == 0)) {
+        if (!kUsingConstantSpaceBeg && kRandomShuffleChunks)
           // The random state is initialized from ASLR.
           region->rand_state = static_cast<u32>(region_beg >> 12);
+        // Postpone the first release to OS attempt for ReleaseToOSIntervalMs,
+        // preventing just allocated memory from being released sooner than
+        // necessary and also preventing extraneous ReleaseMemoryPagesToOS calls
+        // for short lived processes.
+        region->rtoi.last_release_at_ns = NanoTime();
+      }
       // Do the mmap for the user memory.
       uptr map_size = kUserMapSize;
       while (new_space_end > region->mapped_user + map_size)
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_flags.inc b/compiler-rt/lib/sanitizer_common/sanitizer_flags.inc
index eab33ab4562..21876e08f4a 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_flags.inc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_flags.inc
@@ -129,11 +129,11 @@ COMMON_FLAG(uptr, soft_rss_limit_mb, 0,
             " This limit does not affect memory allocations other than"
             " malloc/new.")
 COMMON_FLAG(bool, heap_profile, false, "Experimental heap profiler, asan-only")
-COMMON_FLAG(s32, allocator_release_to_os_interval_ms, kReleaseToOSIntervalNever,
-            "Experimental. Only affects a 64-bit allocator. If set, tries to "
-            "release unused memory to the OS, but not more often than this "
-            "interval (in milliseconds). Negative values mean do not attempt "
-            "to release memory to the OS.\n")
+COMMON_FLAG(s32, allocator_release_to_os_interval_ms, 5000,
+            "Only affects a 64-bit allocator. If set, tries to release unused "
+            "memory to the OS, but not more often than this interval (in "
+            "milliseconds). Negative values mean do not attempt to release "
+            "memory to the OS.\n")
 COMMON_FLAG(bool, can_use_proc_maps_statm, true,
             "If false, do not attempt to read /proc/maps/statm."
             " Mostly useful for testing sanitizers.")