perf: set static mmap threshold on gnu target env by default

src/malloc.rs

@@ -0,0 +1,14 @@
+use std::os::raw::c_int;
+
+const M_MMAP_THRESHOLD: c_int = -3;
+
+extern "C" {
+    fn mallopt(param: c_int, value: c_int) -> c_int;
+}
+
+/// Prevents glibc from hoarding memory via memory fragmentation.
+pub fn limit_mmap_threshold(threshold: i32) {
+    unsafe {
+        mallopt(M_MMAP_THRESHOLD, threshold as c_int);
+    }
+}