Overhaul memory allocation model

This commit makes several fundamental changes to memory handling:

- the frame allocator is now only an allocator for free frames, and does
  not track used frames.
- the frame allocator now stores its free list inside the free frames
  themselves, as a hybrid stack/span model.
  - This has the implication that all frames must currently fit within
    the offset area.
- kutil has a new allocator interface, which is the only allowed way for
  any code outside of src/kernel to allocate. Code under src/kernel
  _may_ use new/delete, but should prefer the allocator interface.
- the heap manager has become heap_allocator, which is merely an
  implementation of kutil::allocator which doles out sections of a given
  address range.
- the heap manager now only writes block headers when necessary,
  avoiding page faults until they're actually needed
- page_manager now has a page fault handler, which checks with the
  address_manager to see if the address is known, and provides a frame
  mapping if it is, allowing heap manager to work with its entire
  address size from the start. (Currently 32GiB.)

src/kernel/frame_allocator.cpp

@@ -0,0 +1,93 @@
+#include "kutil/assert.h"
+#include "kutil/memory.h"
+#include "frame_allocator.h"
+
+using memory::frame_size;
+using memory::page_offset;
+using frame_block_node = kutil::list_node<frame_block>;
+
+frame_allocator g_frame_allocator;
+
+int
+frame_block::compare(const frame_block *rhs) const
+{
+	if (address < rhs->address)
+		return -1;
+	else if (address > rhs->address)
+		return 1;
+	return 0;
+}
+
+
+frame_allocator::raw_alloc::raw_alloc(frame_allocator &fa) : m_fa(fa) {}
+
+void *
+frame_allocator::raw_alloc::allocate(size_t size)
+{
+	kassert(size <= frame_size, "Raw allocator only allocates a single page");
+
+	uintptr_t addr = 0;
+	if (size <= frame_size)
+		m_fa.allocate(1, &addr);
+	return reinterpret_cast<void*>(addr + page_offset);
+}
+
+void
+frame_allocator::raw_alloc::free(void *p)
+{
+	m_fa.free(reinterpret_cast<uintptr_t>(p), 1);
+}
+
+
+frame_allocator::frame_allocator() :
+	m_raw_alloc(*this)
+{
+}
+
+size_t
+frame_allocator::allocate(size_t count, uintptr_t *address)
+{
+	kassert(!m_free.empty(), "frame_allocator::pop_frames ran out of free frames!");
+	if (m_free.empty())
+		return 0;
+
+	auto *first = m_free.front();
+
+	if (count >= first->count) {
+		*address = first->address;
+		m_free.remove(first);
+		return first->count;
+	} else {
+		first->count -= count;
+		*address = first->address + (first->count * frame_size);
+		return count;
+	}
+}
+
+inline uintptr_t end(frame_block *node) { return node->address + node->count * frame_size; }
+
+void
+frame_allocator::free(uintptr_t address, size_t count)
+{
+	frame_block_node *node =
+		reinterpret_cast<frame_block_node*>(address + page_offset);
+
+	kutil::memset(node, 0, sizeof(frame_block_node));
+	node->address = address;
+	node->count = count;
+
+	m_free.sorted_insert(node);
+
+	frame_block_node *next = node->next();
+	if (next && end(node) == next->address) {
+		node->count += next->count;
+		m_free.remove(next);
+	}
+
+	frame_block_node *prev = node->prev();
+	if (prev && end(prev) == address) {
+		prev->count += node->count;
+		m_free.remove(node);
+	}
+}
+