From 07577620837cd9d550ec15e00694fc10fe957247 Mon Sep 17 00:00:00 2001
From: Matthew Parkinson <mattpark@microsoft.com>
Date: Mon, 7 Jun 2021 09:21:22 +0100
Subject: [PATCH] Enable overcommit for heuristic on Linux

---
 src/pal/pal_linux.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/pal/pal_linux.h b/src/pal/pal_linux.h
index f9ad8b2..8104b33 100644
--- a/src/pal/pal_linux.h
+++ b/src/pal/pal_linux.h
@@ -28,6 +28,14 @@ namespace snmalloc
     static constexpr size_t page_size =
       Aal::aal_name == PowerPC ? 0x10000 : PALPOSIX::page_size;
 
+    /**
+     * Linux requires an explicit no-reserve flag in `mmap` to guarantee lazy
+     * commit if /proc/sys/vm/overcommit_memory is set to `heuristic` (0).
+     *
+     *   https://www.kernel.org/doc/html/latest/vm/overcommit-accounting.html
+     */
+    static constexpr int default_mmap_flags = MAP_NORESERVE;
+
     /**
      * OS specific function for zeroing memory.
      *