Add a simple MallocMmapGuard

2 files changed, 49 insertions, 0 deletions

diff --git a/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.cpp b/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.cpp
new file mode 100644
index 00000000000..2b932981823
--- /dev/null
+++ b/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.cpp
@@ -0,0 +1,22 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+#include "malloc_mmap_guard.h"
+#include <malloc.h>
+#include <limits>
+#include <cassert>
+
+namespace vespalib {
+
+MallocMmapGuard::MallocMmapGuard(size_t mmapLimit) :
+    _threadId(std::this_thread::get_id())
+{
+    int limit = mmapLimit <= std::numeric_limits<int>::max() ? mmapLimit : std::numeric_limits<int>::max();
+    mallopt(M_MMAP_THRESHOLD, limit);
+}
+
+MallocMmapGuard::~MallocMmapGuard()
+{
+    assert(_threadId == std::this_thread::get_id());
+    mallopt(M_MMAP_THRESHOLD, -1);
+}
+
+}
diff --git a/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.h b/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.h
new file mode 100644
index 00000000000..3cf26202f9b
--- /dev/null
+++ b/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.h
@@ -0,0 +1,27 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+#pragma once
+
+#include <thread>
+
+namespace vespalib {
+
+/**
+ * Provides a hint to malloc implementation that all allocations in the scope of this guard
+ * will use mmap directly for allocation larger than the givem limit.
+ * The effect is implementation dependent. vespamalloc applies this only for the calling thread.
+ **/
+class MallocMmapGuard
+{
+public:
+    MallocMmapGuard(size_t mmapLimit);
+    MallocMmapGuard(const MallocMmapGuard &) = delete;
+    MallocMmapGuard & operator=(const MallocMmapGuard &) = delete;
+    MallocMmapGuard(MallocMmapGuard &&) = delete;
+    MallocMmapGuard & operator=(MallocMmapGuard &&) = delete;
+    ~MallocMmapGuard();
+private:
+    std::thread::id _threadId;
+};
+
+} // namespace vespalib
+