From 263e9562c0679efbd320a42475f563ae716db270 Mon Sep 17 00:00:00 2001
From: Nathaniel Filardo <nfilardo@microsoft.com>
Date: Fri, 20 Nov 2020 02:08:23 +0000
Subject: [PATCH] NFC: Feed Pagemap its primitive allocator as template arg

This will let us use Pagemaps further down the dependency stack (specifically,
we're going to want a Pagemap inside the AddressSpaceManager) by letting us
manually tie the knot rather than rely on GlobalVirtual and
default_memory_provider() being defined by the time we want a Pagemap.
---
 src/mem/chunkmap.h               |  2 +-
 src/mem/largealloc.h             |  9 +++++++++
 src/mem/pagemap.h                | 21 ++++++++++++++++++---
 src/test/func/pagemap/pagemap.cc |  2 +-
 4 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/src/mem/chunkmap.h b/src/mem/chunkmap.h
index 8d9f976..37a35db 100644
--- a/src/mem/chunkmap.h
+++ b/src/mem/chunkmap.h
@@ -81,7 +81,7 @@ namespace snmalloc
   using ChunkmapPagemap = std::conditional_t<
     CHUNKMAP_USE_FLATPAGEMAP,
     FlatPagemap<SUPERSLAB_BITS, uint8_t>,
-    Pagemap<SUPERSLAB_BITS, uint8_t, 0>>;
+    Pagemap<SUPERSLAB_BITS, uint8_t, 0, DefaultPrimAlloc>>;
 
   struct ForChunkmap
   {};
diff --git a/src/mem/largealloc.h b/src/mem/largealloc.h
index c3fbdc8..b3433b5 100644
--- a/src/mem/largealloc.h
+++ b/src/mem/largealloc.h
@@ -390,4 +390,13 @@ namespace snmalloc
   {
     return *(Singleton<GlobalVirtual*, GlobalVirtual::make>::get());
   }
+
+  struct DefaultPrimAlloc
+  {
+    template<typename T, size_t alignment, typename... Args>
+    static T* alloc_chunk(Args&&... args)
+    {
+      return default_memory_provider().alloc_chunk<T, alignment>(args...);
+    }
+  };
 } // namespace snmalloc
diff --git a/src/mem/pagemap.h b/src/mem/pagemap.h
index ad462b7..f15502e 100644
--- a/src/mem/pagemap.h
+++ b/src/mem/pagemap.h
@@ -53,8 +53,24 @@ namespace snmalloc
    * allocators do not interact with this directly but rather via the
    * static ChunkMap object, which encapsulates knowledge about the
    * pagemap's parametric type T.
+   *
+   * The other template paramters are...
+   *
+   *   GRANULARITY_BITS: the log2 of the size in bytes of the address space
+   *   granule associated with each entry.
+   *
+   *   default_content: An initial value of T (typically "0" or something akin)
+   *
+   *   PrimAlloc: A class used to source PageMap-internal memory; it must have a
+   *   method callable as if it had the following type:
+   *
+   *      template<typename T, size_t alignment> static T* alloc_chunk(void);
    */
-  template<size_t GRANULARITY_BITS, typename T, T default_content>
+  template<
+    size_t GRANULARITY_BITS,
+    typename T,
+    T default_content,
+    typename PrimAlloc>
   class Pagemap
   {
   private:
@@ -154,8 +170,7 @@ namespace snmalloc
         if (e->compare_exchange_strong(
               value, LOCKED_ENTRY, std::memory_order_relaxed))
         {
-          auto& v = default_memory_provider();
-          value = v.alloc_chunk<PagemapEntry, OS_PAGE_SIZE>();
+          value = PrimAlloc::template alloc_chunk<PagemapEntry, OS_PAGE_SIZE>();
           e->store(value, std::memory_order_release);
         }
         else
diff --git a/src/test/func/pagemap/pagemap.cc b/src/test/func/pagemap/pagemap.cc
index 571cff0..ad96170 100644
--- a/src/test/func/pagemap/pagemap.cc
+++ b/src/test/func/pagemap/pagemap.cc
@@ -15,7 +15,7 @@ using namespace snmalloc;
 using T = size_t;
 static constexpr size_t GRANULARITY_BITS = 9;
 static constexpr T PRIME = 251;
-Pagemap<GRANULARITY_BITS, T, 0> pagemap_test;
+Pagemap<GRANULARITY_BITS, T, 0, DefaultPrimAlloc> pagemap_test;
 
 int main(int argc, char** argv)
 {