Let default limit be 1G, and add extra comment about usage and non-usage.

4 files changed, 7 insertions, 5 deletions

diff --git a/staging_vespalib/src/tests/shutdownguard/shutdownguard_test.cpp b/staging_vespalib/src/tests/shutdownguard/shutdownguard_test.cpp
index 0fb2dfdda4b..348e9bbd503 100644
--- a/staging_vespalib/src/tests/shutdownguard/shutdownguard_test.cpp
+++ b/staging_vespalib/src/tests/shutdownguard/shutdownguard_test.cpp
@@ -40,4 +40,4 @@ TEST("test malloc mmap guard") {
     MallocMmapGuard guard(0x100000);
 }
 
-TEST_MAIN() { TEST_RUN_ALL(); }
\ No newline at end of file
+TEST_MAIN() { TEST_RUN_ALL(); }
diff --git a/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.cpp b/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.cpp
index 2b932981823..0ced160fda2 100644
--- a/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.cpp
+++ b/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.cpp
@@ -1,5 +1,6 @@
 // Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 #include "malloc_mmap_guard.h"
+#include <vespa/vespalib/util/size_literals.h>
 #include <malloc.h>
 #include <limits>
 #include <cassert>
@@ -16,7 +17,7 @@ MallocMmapGuard::MallocMmapGuard(size_t mmapLimit) :
 MallocMmapGuard::~MallocMmapGuard()
 {
     assert(_threadId == std::this_thread::get_id());
-    mallopt(M_MMAP_THRESHOLD, -1);
+    mallopt(M_MMAP_THRESHOLD, 1_Gi);
 }
 
 }
diff --git a/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.h b/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.h
index 3cf26202f9b..03e6d38c03c 100644
--- a/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.h
+++ b/staging_vespalib/src/vespa/vespalib/util/malloc_mmap_guard.h
@@ -7,7 +7,9 @@ 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.
+ * will use mmap directly for allocation larger than the given limit.
+ * NB !! Note that guards can not be nested. Intention is to use around third party libraries where
+ * you do not control allocation yourself.
  * The effect is implementation dependent. vespamalloc applies this only for the calling thread.
  **/
 class MallocMmapGuard
@@ -24,4 +26,3 @@ private:
 };
 
 } // namespace vespalib
-
diff --git a/vespamalloc/src/vespamalloc/malloc/threadpool.hpp b/vespamalloc/src/vespamalloc/malloc/threadpool.hpp
index a3691a496dd..e9b9fabebdc 100644
--- a/vespamalloc/src/vespamalloc/malloc/threadpool.hpp
+++ b/vespamalloc/src/vespamalloc/malloc/threadpool.hpp
@@ -86,7 +86,7 @@ mallocHelper(size_t exactSize,
 template <typename MemBlockPtrT, typename ThreadStatT >
 ThreadPoolT<MemBlockPtrT, ThreadStatT>::ThreadPoolT() :
     _allocPool(nullptr),
-    _mmapLimit(-1),
+    _mmapLimit(0x40000000),
     _threadId(0),
     _osThreadId(0)
 {