Switch uer heap to linked list allocator

1 files changed, 97 insertions, 21 deletions

diff --git a/arch/x86_64/include/arch/memory/heap/user_heap_allocator.hpp b/arch/x86_64/include/arch/memory/heap/user_heap_allocator.hpp
index 9d00c19..d698888 100644
--- a/arch/x86_64/include/arch/memory/heap/user_heap_allocator.hpp
+++ b/arch/x86_64/include/arch/memory/heap/user_heap_allocator.hpp
@@ -1,16 +1,14 @@
 #ifndef TEACHOS_ARCH_X86_64_MEMORY_HEAP_USER_HEAP_ALLOCATOR_HPP
 #define TEACHOS_ARCH_X86_64_MEMORY_HEAP_USER_HEAP_ALLOCATOR_HPP
 
-#include "arch/memory/heap/heap_allocator.hpp"
-
-#include <atomic>
-#include <cstdint>
+#include "arch/memory/heap/memory_block.hpp"
+#include "arch/stl/mutex.hpp"
 
 namespace teachos::arch::memory::heap
 {
   /**
-   * @brief Simple heap allocator, which allocates linearly and leaks all allocated memory, because it does not really
-   * deallocate anything.
+   * @brief Sorted by address list of memory holes (free memory). Uses free holes itself to save the information,
+   * containing the size and pointer to the next hole. Resulting in a singly linked list.
    */
   struct user_heap_allocator
   {
@@ -20,31 +18,109 @@ namespace teachos::arch::memory::heap
      * @param heap_start Start of the allocatable heap area
      * @param heap_end End of the allocatable heap area (Start + Size)
      */
-    user_heap_allocator(std::size_t heap_start, std::size_t heap_end)
-        : heap_start{heap_start}
-        , heap_end{heap_end}
-        , next{heap_start}
-    {
-      // Nothing to do
-    }
+    user_heap_allocator(std::size_t heap_start, std::size_t heap_end);
 
+    /**
+     * @copybrief heap_allocator::allocate
+     *
+     * @note The specified size is used to find a free memory block with the exact same size, meaning we can remove that
+     * free memory block from the free list and simply return its address. Or it has to be big enough to hold the size
+     * and alteast enough memory for another free memory block entry (16 bytes). If the amount of memory of that free
+     * memory block is in between we cannot use it for our allocation, because we could only return it to the user, but
+     * the additional bytes, could not be used to create a free memory block. Additionaly the user couldn't know
+     * they received more memory than wanted. Therefore the memory would simply be unused and because it is neither
+     * allocated nor deallocated would never be indexed by the free memory list. We would therefore permanently loose
+     * that memory, to prevent that allocation into free memory blocks like that are impossible.
+     */
     [[gnu::section(".user_text")]]
     auto allocate(std::size_t size) -> void *;
 
+    [[gnu::section(".user_text")]]
+    auto deallocate(void * pointer) noexcept -> void;
+
+  private:
     /**
-     * @copybrief heap_allocator::deallocate
+     * @brief Returns the smallest allocatable block of heap memory.
      *
-     * @note Simply does nothing, because this allocator leaks all memory
+     * @return Smallest allocatable block of heap memory.
+     */
+    [[gnu::section(".user_text")]] auto constexpr min_allocatable_size() -> std::size_t { return sizeof(memory_block); }
+
+    /**
+     * @brief Removes a free memory block from the free list and returns its address so the caller can allocate into it.
+     *
+     * @param previous_block Free memory block before the block to allocate in our heap memory. Was to small to
+     * allocate the required size into.
+     * @param current_block Free memory block we want to remove from the free list and return for the allocation.
+     *
+     * @return Previous start address of the memory block we removed, because it can now be used for the allocation.
      */
     [[gnu::section(".user_text")]]
-    auto deallocate(void * pointer) noexcept -> void;
+    auto remove_free_memory_block(memory_block * previous_block, memory_block * current_block) -> void *;
 
-  private:
-    std::size_t heap_start;     ///< Start of the allocatable heap area
-    std::size_t heap_end;       ///< End of the allocatable heap area
-    std::atomic_uint64_t next;  ///< Current address, which is the start of still unused allocatable heap area
-  };
+    /**
+     * @brief Splits the given free memory block into two, where the latter block keeps being free and the first
+     * part will be used for the allocation.
+     *
+     * @param previous_block Free memory block before the block to allocate in our heap memory. Was to small to
+     * allocate the required size into.
+     * @param current_block Free memory block we want to split into a size part for the allocation and the rest for
+     * future allocations.
+     * @param size Size we want to allocate at the start of the free memory block.
+     *
+     * @return Previous start address of the memory block we just split, because it can now be used for the allocation.
+     */
+    [[gnu::section(".user_text")]]
+    auto split_free_memory_block(memory_block * previous_block, memory_block * current_block, std::size_t size)
+        -> void *;
 
+    /**
+     * @brief Removes a free memory block from the free list and returns its address so the caller can allocate into it.
+     *
+     * @param previous_block Free memory block before the block to allocate in our heap memory. Was to small to
+     * allocate the required size into.
+     * @param current_block Free memory block we want to remove from the free list and return for the allocation.
+     * @param new_block Replaces the current block with the given new block can be nullptr, meaning the free list will
+     * end here.
+     *
+     * @return Previous start address of the memory block we removed, because it can now be used for the allocation.
+     */
+    [[gnu::section(".user_text")]]
+    auto replace_free_memory_block(memory_block * previous_block, memory_block * current_block,
+                                   memory_block * new_block) -> void *;
+
+    /**
+     * @brief Combines multiple free memory blocks into one if they are adjacent.
+     *
+     * @note The internal algorithm for recombination functions like this:
+     * 1. Check if there is even any memory left, if not the first entry of our linked list should be a nullptr and
+     * we can therefore set the first entry to our newly created entry. This entry is created in the now deallocated
+     * memory area.
+     * 2. If there are more blocks but neither the previous nor the current block are adjacent, we simply create a
+     * new free memory block of the given size and set the previous next to our block and the next of our block to
+     * the current block.
+     * 3. If the current block is adjacent the start address of the newly created block stays the same, but the size
+     * increases by the amount in the current memory block header. After reading it we also clear the header.
+     * 4. If the previous block is adjacent the size of the previous block simply increases to include the given
+     * size as well.
+     * 5. If the previous block is directly in our start address, so they overlap then it has to mean some or all of
+     * the region we are trying to deallocate has been freed before. Which would result in a double free therefore
+     * we halt the execution of the program.
+     *
+     * @param previous_block Free memory block before the block to deallocate in our heap memory.
+     * @param current_block Free memory block after the block to deallocate in our heap memory.
+     * @param pointer Block to deallocate.
+     * @param size Size of the block we want to deallocate.
+     */
+    [[gnu::section(".user_text")]]
+    auto coalesce_free_memory_block(memory_block * previous_block, memory_block * current_block, void * pointer,
+                                    std::size_t size) -> void;
+
+    std::size_t heap_start;  ///< Start of the allocatable heap area.
+    std::size_t heap_end;    ///< End of the allocatable heap area.
+    memory_block * first;    ///< First free entry in our memory.
+    stl::mutex mutex;        ///< Mutex to ensure only one thread calls allocate or deallocate at once.
+  };
 }  // namespace teachos::arch::memory::heap
 
 #endif  // TEACHOS_ARCH_X86_64_MEMORY_HEAP_USER_HEAP_ALLOCATOR_HPP