Heap: Use LinkedList instead of doing things manually

kernel/src/memory/Heap.cpp

@@ -5,6 +5,7 @@
 #include "memory/KernelVM.h"
 #include "memory/MemoryManager.h"
 #include <luna/Alignment.h>
+#include <luna/LinkedList.h>
 #include <luna/SafeArithmetic.h>
 #include <luna/String.h>
 #include <luna/SystemError.h>
@@ -18,20 +19,17 @@ static constexpr usize BLOCK_DEAD = 0xdeaddeaddeaddead;
 
 static constexpr usize MINIMUM_PAGES_PER_ALLOCATION = 4;
 
-struct HeapBlock
+struct HeapBlock : DoublyLinkedListNode<HeapBlock>
 {
     usize req_size;
     usize full_size;
     int status;
-    HeapBlock* next;
-    HeapBlock* last;
     usize magic;
 };
 
 static_assert(sizeof(HeapBlock) == 48UL);
 
-static HeapBlock* heap_start = nullptr;
+static DoublyLinkedList<HeapBlock> heap;
-static HeapBlock* heap_end = nullptr;
 
 static Result<HeapBlock*> allocate_pages(usize count)
 {
@@ -96,7 +94,8 @@ static Result<HeapBlock*> split(HeapBlock* block, usize size)
     const usize old_size =
         block->full_size; // Save the old value of this variable since we are going to use it after modifying it
 
-    if (available < (size + sizeof(HeapBlock))) return err(0); // This error is not propagated.
+    if (available < (size + sizeof(HeapBlock)))
+        return err(ENONE); // This block hasn't got enough free space to hold the requested size.
 
     const usize offset = get_fair_offset_to_split_at(block, size + sizeof(HeapBlock));
     block->full_size = offset; // shrink the old block to fit this offset
@@ -106,24 +105,20 @@ static Result<HeapBlock*> split(HeapBlock* block, usize size)
     new_block->magic = BLOCK_MAGIC;
     new_block->status = (block->status & BLOCK_END_MEM) ? BLOCK_END_MEM : 0;
     new_block->full_size = old_size - (offset + sizeof(HeapBlock));
-    new_block->next = block->next;
+    heap.append_after(block, new_block);
-    new_block->last = block;
 
-    block->status &= ~BLOCK_END_MEM; // this block is no longer the last block in this memory range
+    block->status &= ~BLOCK_END_MEM; // this block is no longer the last block in its memory range
-    block->next = new_block;
 
     return new_block;
 }
 
 static Result<void> combine_forward(HeapBlock* block)
 {
-    HeapBlock* const next = block->next;
+    // The caller needs to ensure there is a next block.
-    if (next == heap_end) heap_end = block;
+    HeapBlock* const next = heap.next(block).value();
+    heap.remove(next);
     next->magic = BLOCK_DEAD;
 
-    block->next = block->next->next;
-    if (block->next) block->next->last = block;
-
     if (next->status & BLOCK_END_MEM)
     {
         if (next->status & BLOCK_START_MEM)
@@ -142,13 +137,11 @@ static Result<void> combine_forward(HeapBlock* block)
 
 static Result<HeapBlock*> combine_backward(HeapBlock* block)
 {
-    HeapBlock* const last = block->last;
+    // The caller needs to ensure there is a last block.
-    if (block == heap_end) heap_end = last;
+    HeapBlock* const last = heap.previous(block).value();
+    heap.remove(block);
     block->magic = BLOCK_DEAD;
 
-    last->next = block->next;
-    if (last->next) last->next->last = last;
-
     if (block->status & BLOCK_END_MEM)
     {
         if (block->status & BLOCK_START_MEM)
@@ -171,7 +164,7 @@ Result<void*> kmalloc(usize size)
 
     size = align_up(size, 16UL);
 
-    if (!heap_start)
+    if (!heap.first().has_value())
     {
         const usize pages = get_pages_for_allocation(size + sizeof(HeapBlock));
         HeapBlock* const block = TRY(allocate_pages(pages));
@@ -179,15 +172,10 @@ Result<void*> kmalloc(usize size)
         block->full_size = (pages * ARCH_PAGE_SIZE) - sizeof(HeapBlock);
         block->magic = BLOCK_MAGIC;
         block->status = BLOCK_START_MEM | BLOCK_END_MEM;
-        block->next = block->last = nullptr;
+        heap.append(block);
-        heap_start = block;
-
-        check(!heap_end);
-
-        heap_end = heap_start;
     }
 
-    HeapBlock* block = heap_start;
+    HeapBlock* block = heap.first().value();
     while (block)
     {
         // Trying to find a free block...
@@ -195,7 +183,7 @@ Result<void*> kmalloc(usize size)
         {
             if (block->full_size < size)
             {
-                block = block->next; // Let's not try to split this block, it's not big enough
+                block = heap.next(block).value_or(nullptr);
                 continue;
             }
             break; // We found a free block that's big enough!!
@@ -203,10 +191,10 @@ Result<void*> kmalloc(usize size)
         auto rc = split(block, size);
         if (rc.has_value())
         {
-            block = rc.release_value(); // We managed to get a free block from a larger used block!!
+            block = rc.value(); // We managed to get a free block from a larger used block!!
             break;
         }
-        block = block->next;
+        block = heap.next(block).value_or(nullptr);
     }
 
     if (!block) // No free blocks, let's allocate a new one
@@ -217,11 +205,7 @@ Result<void*> kmalloc(usize size)
         block->full_size = (pages * ARCH_PAGE_SIZE) - sizeof(HeapBlock);
         block->magic = BLOCK_MAGIC;
         block->status = BLOCK_START_MEM | BLOCK_END_MEM;
-        block->next = nullptr;
+        heap.append(block);
-        block->last = heap_end;
-        heap_end->next = block;
-
-        heap_end = block;
     }
 
     block->req_size = size;
@@ -257,13 +241,15 @@ Result<void> kfree(void* ptr)
     else
         block->status &= ~BLOCK_USED;
 
-    if (block->next && is_block_free(block->next))
+    auto maybe_next = heap.next(block);
+    if (maybe_next.has_value() && is_block_free(maybe_next.value()))
     {
         // The next block is also free, thus we can merge!
         TRY(combine_forward(block));
     }
 
-    if (block->last && is_block_free(block->last))
+    auto maybe_last = heap.previous(block);
+    if (maybe_last.has_value() && is_block_free(maybe_last.value()))
     {
         // The last block is also free, thus we can merge!
         block = TRY(combine_backward(block));
@@ -271,10 +257,7 @@ Result<void> kfree(void* ptr)
 
     if ((block->status & BLOCK_START_MEM) && (block->status & BLOCK_END_MEM))
     {
-        if (block == heap_start) heap_start = block->next;
+        heap.remove(block);
-        if (block == heap_end) heap_end = block->last;
-        if (block->last) block->last->next = block->next;
-        if (block->next) block->next->last = block->last;
         TRY(release_pages(block, get_blocks_from_size(block->full_size + sizeof(HeapBlock), ARCH_PAGE_SIZE)));
     }
 
@@ -337,14 +320,14 @@ Result<void*> kcalloc(usize nmemb, usize size)
 void dump_heap_usage()
 {
     kdbgln("-- Dumping usage stats for kernel heap:");
-    if (!heap_start)
+    if (!heap.count())
     {
         kdbgln("- Heap is not currently being used");
         return;
     }
     usize alloc_total = 0;
     usize alloc_used = 0;
-    HeapBlock* block = heap_start;
+    HeapBlock* block = heap.first().value();
     while (block)
     {
         if (is_block_free(block))
@@ -358,7 +341,7 @@ void dump_heap_usage()
             alloc_total += block->full_size + sizeof(HeapBlock);
             alloc_used += block->req_size;
         }
-        block = block->next;
+        block = heap.next(block).value_or(nullptr);
     }
 
     kdbgln("-- Total memory allocated for heap: %zu bytes", alloc_total);