[v18.x backport] child_process: improve spawn performance on Linux

common.gypi

@@ -36,7 +36,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.26',
+    'v8_embedder_string': '-node.27',
 
     ##### V8 defaults for Node.js #####
 

deps/v8/BUILD.gn

@@ -82,6 +82,17 @@ declare_args() {
   # Sets -dENABLE_HUGEPAGE
   v8_enable_hugepage = false
 
+  # Sets -dV8_ENABLE_PRIVATE_MAPPING_FORK_OPTIMIZATION.
+  #
+  # This flag speeds up the performance of fork/execve on Linux systems for
+  # embedders which use it (like Node.js). It works by marking the pages that
+  # V8 allocates as MADV_DONTFORK. Without MADV_DONTFORK, the Linux kernel
+  # spends a long time manipulating page mappings on fork and exec which the
+  # child process doesn't generally need to access.
+  #
+  # See v8:7381 for more details.
+  v8_enable_private_mapping_fork_optimization = false
+
   # Sets -dENABLE_HANDLE_ZAPPING.
   v8_enable_handle_zapping = !is_on_release_branch || is_debug
 
@@ -862,6 +873,9 @@ config("features") {
   if (v8_enable_hugepage) {
     defines += [ "ENABLE_HUGEPAGE" ]
   }
+  if (v8_enable_private_mapping_fork_optimization) {
+    defines += [ "V8_ENABLE_PRIVATE_MAPPING_FORK_OPTIMIZATION" ]
+  }
   if (v8_enable_object_print) {
     defines += [ "OBJECT_PRINT" ]
   }

deps/v8/src/base/platform/platform-posix.cc

@@ -174,6 +174,12 @@ void* Allocate(void* hint, size_t size, OS::MemoryPermission access,
   int flags = GetFlagsForMemoryPermission(access, page_type);
   void* result = mmap(hint, size, prot, flags, kMmapFd, kMmapFdOffset);
   if (result == MAP_FAILED) return nullptr;
+
+#if V8_ENABLE_PRIVATE_MAPPING_FORK_OPTIMIZATION
+  // This is advisory, so we ignore errors.
+  madvise(result, size, MADV_DONTFORK);
+#endif
+
 #if ENABLE_HUGEPAGE
   if (result != nullptr && size >= kHugePageSize) {
     const uintptr_t huge_start =

tools/v8_gypfiles/features.gypi

@@ -68,6 +68,20 @@
       }, {
         'v8_enable_system_instrumentation': 0,
       }],
+      ['OS=="linux"', {
+        # Sets -dV8_ENABLE_PRIVATE_MAPPING_FORK_OPTIMIZATION.
+        #
+        # This flag speeds up the performance of fork/execve on Linux systems for
+        # embedders which use it (like Node.js). It works by marking the pages that
+        # V8 allocates as MADV_DONTFORK. Without MADV_DONTFORK, the Linux kernel
+        # spends a long time manipulating page mappings on fork and exec which the
+        # child process doesn't generally need to access.
+        #
+        # See v8:7381 for more details.
+        'v8_enable_private_mapping_fork_optimization': 1,
+      }, {
+        'v8_enable_private_mapping_fork_optimization': 0,
+      }],
     ],
     'is_debug%': 0,
 
@@ -310,6 +324,9 @@
       ['v8_enable_hugepage==1', {
         'defines': ['ENABLE_HUGEPAGE',],
       }],
+      ['v8_enable_private_mapping_fork_optimization==1', {
+        'defines': ['V8_ENABLE_PRIVATE_MAPPING_FORK_OPTIMIZATION'],
+      }],
       ['v8_enable_vtunejit==1', {
         'defines': ['ENABLE_VTUNE_JIT_INTERFACE',],
       }],