const runtime._MADV_COLLAPSE 2 uses runtime (current package) defs_linux_amd64.go#L27: _MADV_COLLAPSE = 0x19 mem_linux.go#L147: madvise(v, n, _MADV_COLLAPSE)
The pages are generated with Golds v0.8.4. (GOOS=linux GOARCH=amd64)