From 272fd42c970d48d526f0d5ab8dc4fef4d8f177e7 Mon Sep 17 00:00:00 2001
From: Nick Greenfield <boyd.greenfield@gmail.com>
Date: Wed, 23 Jul 2014 11:25:21 -0700
Subject: [PATCH] Add automatic MAP_POPULATE flag for opening read_only
 (MAP_PRIVATE) and shared (MAP_SHARED) mmap files.

---
 lib/posix/posix.nim   | 2 ++
 lib/pure/memfiles.nim | 4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/posix/posix.nim b/lib/posix/posix.nim
index 8e66336c2e..17bcc420ed 100644
--- a/lib/posix/posix.nim
+++ b/lib/posix/posix.nim
@@ -1375,6 +1375,8 @@ var
     ## Share changes.
   MAP_PRIVATE* {.importc, header: "<sys/mman.h>".}: cint
     ## Changes are private.
+  MAP_POPULATE* {.importc, header: "<sys/mman.h>".}: cint
+    ## Populate (prefault) page tables for a mapping.
   MAP_FIXED* {.importc, header: "<sys/mman.h>".}: cint
     ## Interpret addr exactly.
   MS_ASYNC* {.importc, header: "<sys/mman.h>".}: cint
diff --git a/lib/pure/memfiles.nim b/lib/pure/memfiles.nim
index 31fefc6c82..ffeb0beffe 100644
--- a/lib/pure/memfiles.nim
+++ b/lib/pure/memfiles.nim
@@ -54,7 +54,7 @@ proc mapMem*(m: var TMemFile, mode: TFileMode = fmRead,
       nil,
       mappedSize,
       if readonly: PROT_READ else: PROT_READ or PROT_WRITE,
-      if readonly: MAP_PRIVATE else: MAP_SHARED,
+      if readonly: (MAP_PRIVATE or MAP_POPULATE) else: (MAP_SHARED or MAP_POPULATE),
       m.handle, offset)
     if result == cast[pointer](MAP_FAILED):
       osError(osLastError())
@@ -207,7 +207,7 @@ proc open*(filename: string, mode: TFileMode = fmRead,
       nil,
       result.size,
       if readonly: PROT_READ else: PROT_READ or PROT_WRITE,
-      if readonly: MAP_PRIVATE else: MAP_SHARED,
+      if readonly: (MAP_PRIVATE or MAP_POPULATE) else: (MAP_SHARED or MAP_POPULATE),
       result.handle,
       offset)