Increase link concurrency for ThinLTO.

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/compiler/compiler.gni")
 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 = [
-      "--mem_per_link_gb=26",
-      "--reserve_mem_gb=20",
-    ]
+    if (use_thin_lto) {
+      _args = [
+        "--mem_per_link_gb=10",
+        "--reserve_mem_gb=10",
+      ]
+    } else {
+      # Full LTO, needs lots of RAM
+      _args = [
+        "--mem_per_link_gb=26",
+        "--reserve_mem_gb=20",
+      ]
+    }
   } else if (is_win) {
     _args = [ "--mem_per_link_gb=5" ]
   } else if (is_mac) {
     _args = [ "--mem_per_link_gb=4" ]
   } else if (is_android && !is_component_build && symbol_level == 2) {
     _args = [ "--mem_per_link_gb=25" ]
   } 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")
 }