From 709bdf9e73bb36fc7bab6b7badaefff4c3a6a393 Mon Sep 17 00:00:00 2001
From: Paul Bone <pbone@mozilla.com>
Date: Tue, 19 Mar 2024 01:42:43 +0000
Subject: [PATCH] Bug 1857841 - pt 7. Also amortise VirtualAlloc in SplitRun()
 r=glandium

Differential Revision: https://phabricator.services.mozilla.com/D195515
---
 memory/build/mozjemalloc.cpp | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/memory/build/mozjemalloc.cpp b/memory/build/mozjemalloc.cpp
index a38bb444a1e1..bab7e057cf69 100644
--- a/memory/build/mozjemalloc.cpp
+++ b/memory/build/mozjemalloc.cpp
@@ -2653,6 +2653,20 @@ bool arena_t::SplitRun(arena_run_t* aRun, size_t aSize, bool aLarge,
                     (CHUNK_MAP_FRESH | CHUNK_MAP_MADVISED)) == 0);
       }
 
+      // Consider committing more pages to amortise calls to VirtualAlloc.
+      // This only makes sense at the edge of our run hence the if condition
+      // here.
+      if (i + j == need_pages) {
+        size_t extra_commit = ExtraCommitPages(j, rem_pages);
+        for (; i + j < need_pages + extra_commit &&
+               (chunk->map[run_ind + i + j].bits &
+                CHUNK_MAP_MADVISED_OR_DECOMMITTED);
+             j++) {
+          MOZ_ASSERT((chunk->map[run_ind + i + j].bits &
+                      (CHUNK_MAP_FRESH | CHUNK_MAP_MADVISED)) == 0);
+        }
+      }
+
       if (!pages_commit(
               (void*)(uintptr_t(chunk) + ((run_ind + i) << gPageSize2Pow)),
               j << gPageSize2Pow)) {