x86_64/memory: introduce frame allocation buffer

3 files changed, 72 insertions, 2 deletions

diff --git a/arch/x86_64/CMakeLists.txt b/arch/x86_64/CMakeLists.txt
index 4d984cf..7f01744 100644
--- a/arch/x86_64/CMakeLists.txt
+++ b/arch/x86_64/CMakeLists.txt
@@ -35,7 +35,7 @@ target_sources("x86_64" PRIVATE
 
 file(GLOB_RECURSE ARCH_HEADERS RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} "include/**.hpp")
 
-target_sources("x86_64" PRIVATE
+target_sources("x86_64" PUBLIC
     FILE_SET HEADERS
     BASE_DIRS "include"
     FILES ${ARCH_HEADERS}
diff --git a/arch/x86_64/include/x86_64/memory/buffered_allocator.hpp b/arch/x86_64/include/x86_64/memory/buffered_allocator.hpp
new file mode 100644
index 0000000..2d05010
--- /dev/null
+++ b/arch/x86_64/include/x86_64/memory/buffered_allocator.hpp
@@ -0,0 +1,67 @@
+#ifndef TEACHOS_X86_64_BUFFERED_ALLOCATOR_HPP
+#define TEACHOS_X86_64_BUFFERED_ALLOCATOR_HPP
+
+#include "kapi/memory.hpp"
+
+#include <algorithm>
+#include <array>
+#include <cstddef>
+
+namespace teachos::memory::x86_64
+{
+
+  template<std::size_t BufferSize>
+  struct buffered_allocator : frame_allocator
+  {
+    explicit buffered_allocator(frame_allocator * underlying)
+        : m_underlying{underlying}
+    {
+      std::ranges::generate(m_pool, [this] { return m_underlying->allocate(); });
+    }
+
+    buffered_allocator(buffered_allocator const &) = delete;
+    buffered_allocator(buffered_allocator &&) = default;
+
+    ~buffered_allocator() override
+    {
+      std::ranges::for_each(m_pool, [this](auto const & maybe_frame) {
+        if (maybe_frame)
+        {
+          m_underlying->release(*maybe_frame);
+        }
+      });
+    }
+
+    auto operator=(buffered_allocator const &) = delete;
+    auto operator=(buffered_allocator &&) = delete;
+
+    auto allocate() -> std::optional<frame> override
+    {
+      auto found = std::ranges::find_if(m_pool, [](auto const & candidate) { return candidate.has_value(); });
+      if (found == std::end(m_pool))
+      {
+        return m_underlying->allocate();
+      }
+      auto frame = found->value();
+      found->reset();
+      return frame;
+    }
+
+    auto release(frame frame) -> void override
+    {
+      auto found = std::ranges::find_if(m_pool, [](auto const & candidate) { return !candidate; });
+      if (found == std::end(m_pool))
+      {
+        return m_underlying->release(frame);
+      }
+      (*found) = frame;
+    }
+
+  private:
+    frame_allocator * m_underlying;
+    std::array<std::optional<frame>, BufferSize> m_pool{};
+  };
+
+}  // namespace teachos::memory::x86_64
+
+#endif
\ No newline at end of file
diff --git a/arch/x86_64/src/kapi/memory.cpp b/arch/x86_64/src/kapi/memory.cpp
index e138641..703b3e1 100644
--- a/arch/x86_64/src/kapi/memory.cpp
+++ b/arch/x86_64/src/kapi/memory.cpp
@@ -5,6 +5,7 @@
 #include "x86_64/boot/boot.hpp"
 #include "x86_64/boot/ld.hpp"
 #include "x86_64/cpu/registers.hpp"
+#include "x86_64/memory/buffered_allocator.hpp"
 #include "x86_64/memory/mmu.hpp"
 #include "x86_64/memory/page_table.hpp"
 #include "x86_64/memory/paging_root.hpp"
@@ -95,7 +96,9 @@ namespace teachos::memory
 
     auto allocator = create_early_frame_allocator();
     enable_cpu_protections();
-    inject_faux_pml4(allocator);
+
+    auto allocation_buffer = x86_64::buffered_allocator<4>{&allocator};
+    inject_faux_pml4(allocation_buffer);
 
     // paging::kernel_mapper kernel(allocator, memory_information);
     // kernel.remap_kernel();