build: Refactor get_concurrent_links.py

build/toolchain/concurrent_links.gni

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This file should only be imported from files that define toolchains.
 # There's no way to enforce this exactly, but all toolchains are processed
 # in the context of the default_toolchain, so we can at least check for that.
 assert(current_toolchain == default_toolchain)
 
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/toolchain.gni")
 
 declare_args() {
   # Limit the number of concurrent links; we often want to run fewer
   # links at once than we do compiles, because linking is memory-intensive.
   # The default to use varies by platform and by the amount of memory
   # available, so we call out to a script to get the right value.
   concurrent_links = -1
 }
 
 if (concurrent_links == -1) {
   if (allow_posix_link_time_opt || is_cfi) {
-    _args = [ "--lto" ]
+    _args = [
+      "--mem_per_link_gb=24",
+      "--reserve_mem_gb=10",
+    ]
+  } else if (is_win) {
+    _args = [ "--mem_per_link_gb=5" ]

[brucedawson, 2016/08/22 19:31:32]

The Windows memory used per linker is highly dependent on the binary being
linked and the build type. The worst-case memory consumption amounts (recorded a
few months ago) are:

64-bit official: 27 GB
32-bit official: 14 GB
64-bit/32-bit static release: 11 GB
64-bit/32-bit component release: 6 GB

These are worst-case numbers, but towards the end of the build process there are
often quite a few worst-cast (test) binaries trying to link simultaneously.

I don't have component debug numbers handy, but I think they are similar to the
component release numbers.

Starting with 5 for compatibility with the existing values is fine, but it might
be worth tweaking after that.

[boliu, 2016/08/22 20:49:03]

This was just intended to be a refactor, without changing behavior for any
platform.

I don't personally build for windows, but hopefully your proposed changes will
get easier after this lands.

+  } else if (is_mac) {
+    _args = [ "--mem_per_link_gb=4" ]
   } else {
     _args = []
   }
 
   # TODO(crbug.com/617429) Pass more build configuration info to the script
   # so that we can compute better values.
   concurrent_links = exec_script("get_concurrent_links.py", _args, "value")
 }