[Sanitizers] Set default allocator_release_to_os_interval_ms to 5 seconds

[alekseyshl]

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.

[alekseyshl]

• Comment edit.

compiler-rt/trunk/lib/sanitizer_common/sanitizer_allocator_primary64.h

NOINLINE bool PopulateFreeArray(AllocatorStats *stat, uptr class_id,
     // region->mutex is held.
     const uptr size = ClassIdToSize(class_id);
     const uptr new_space_beg = region->allocated_user;
     const uptr new_space_end = new_space_beg + requested_count * size;
     const uptr region_beg = GetRegionBeginBySizeClass(class_id);
 
     // Map more space for chunks, if necessary.
     if (new_space_end > region->mapped_user) {
+      if (UNLIKELY(region->mapped_user == 0)) {
         if (!kUsingConstantSpaceBeg && kRandomShuffleChunks)
-        if (UNLIKELY(region->mapped_user == 0))
           // 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)
         map_size += kUserMapSize;
       CHECK_GE(region->mapped_user + map_size, new_space_end);
       if (UNLIKELY(!MapWithCallback(region_beg + region->mapped_user,
                                     map_size)))
         return false;

compiler-rt/trunk/lib/sanitizer_common/sanitizer_flags.inc

COMMON_FLAG(uptr, soft_rss_limit_mb, 0,
             " If non-zero, a background thread is spawned at startup"
             " which periodically reads RSS. If the limit is reached"
             " all subsequent malloc/new calls will fail or return NULL"
             " (depending on the value of allocator_may_return_null)"
             " until the RSS goes below the soft limit."
             " 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.")
 COMMON_FLAG(
     bool, coverage, false,
     "If set, coverage information will be dumped at program shutdown (if the "
     "coverage instrumentation was enabled at compile time).")
 COMMON_FLAG(const char *, coverage_dir, ".",