Kernel: Refactor MemoryManager to use a Bitmap rather than a Vector

This significantly reduces the pressure on the kernel heap when
allocating a lot of pages.

Previously at about 250MB allocated, the free page list would outgrow
the kernel's heap. Given that there is no longer a page list, this does
not happen.

The next barrier will be the kernel memory used by the page records for
in-use memory. This kicks in at about 1GB.

1 files changed, 39 insertions, 0 deletions

diff --git a/Kernel/VM/PhysicalRegion.h b/Kernel/VM/PhysicalRegion.h
new file mode 100644
index 0000000000..d4f4fb1934
--- /dev/null
+++ b/Kernel/VM/PhysicalRegion.h
@@ -0,0 +1,39 @@
+#pragma once
+
+#include <AK/Bitmap.h>
+#include <AK/Retainable.h>
+#include <AK/Retained.h>
+#include <Kernel/PhysicalAddress.h>
+#include <Kernel/VM/PhysicalPage.h>
+
+class PhysicalRegion : public Retainable<PhysicalRegion> {
+    AK_MAKE_ETERNAL
+
+public:
+    static Retained<PhysicalRegion> create(PhysicalAddress lower, PhysicalAddress upper);
+    ~PhysicalRegion() {}
+
+    void expand(PhysicalAddress lower, PhysicalAddress upper);
+    unsigned finalize_capacity();
+
+    PhysicalAddress lower() const { return m_lower; }
+    PhysicalAddress upper() const { return m_upper; }
+    unsigned size() const { return m_pages; }
+    unsigned used() const { return m_used; }
+    unsigned free() const { return m_pages - m_used; }
+    bool contains(PhysicalPage& page) const { return page.paddr() >= m_lower && page.paddr() <= m_upper; }
+
+    RetainPtr<PhysicalPage> take_free_page(bool supervisor);
+    void return_page_at(PhysicalAddress addr);
+    void return_page(PhysicalPage& page) { return_page_at(page.paddr()); }
+
+private:
+    PhysicalRegion(PhysicalAddress lower, PhysicalAddress upper);
+
+    PhysicalAddress m_lower;
+    PhysicalAddress m_upper;
+    unsigned m_pages { 0 };
+    unsigned m_used { 0 };
+    unsigned m_last { 0 };
+    Bitmap m_bitmap;
+};