Kernel: We add FixedWidthAllocators on demand

On SYS_ALLOC we will add a new FixedWidthAllocator if the old ones
are already full or we don't have one with proper size. This allows
arbitary number of allocations as long as you have enough memory
available :)

Next I will be writing a general allocator for allocations larger
than 4096 bytes which should make SYS_ALLOC syscall complete :)

kernel/include/kernel/Memory/FixedWidthAllocator.h

@@ -21,6 +21,9 @@ namespace Kernel
 
 		uint32_t allocation_size() const { return m_allocation_size; }
 
+		uint32_t allocations() const { return m_allocations; }
+		uint32_t max_allocations() const;
+
 	private:
 		struct node
 		{
@@ -44,7 +47,7 @@ namespace Kernel
 		node* m_free_list { nullptr };
 		node* m_used_list { nullptr };
 
-		uint32_t m_allocated { 0 };
+		uint32_t m_allocations { 0 };
 	};
 
 }

kernel/include/kernel/Process.h

@@ -94,7 +94,7 @@ namespace Kernel
 		BAN::String m_working_directory;
 		BAN::Vector<Thread*> m_threads;
 
-		BAN::Vector<FixedWidthAllocator> m_fixed_width_allocators;
+		BAN::LinkedList<FixedWidthAllocator> m_fixed_width_allocators;
 
 		MMU* m_mmu { nullptr };
 		TTY* m_tty { nullptr };

kernel/kernel/Memory/FixedWidthAllocator.cpp

@@ -49,7 +49,7 @@ namespace Kernel
 		, m_allocated_pages(other.m_allocated_pages)
 		, m_free_list(other.m_free_list)
 		, m_used_list(other.m_used_list)
-		, m_allocated(other.m_allocated)
+		, m_allocations(other.m_allocations)
 	{
 		other.m_process = nullptr;
 	}
@@ -81,9 +81,8 @@ namespace Kernel
 
 	paddr_t FixedWidthAllocator::allocate()
 	{
-		// FIXME: We should get allocate more memory if we run out of
-		//        nodes in free list.
-		ASSERT(m_free_list);
+		if (m_free_list == nullptr)
+			return 0;
 
 		node* node = m_free_list;
 
@@ -101,7 +100,7 @@ namespace Kernel
 			m_used_list->prev = node;
 		m_used_list = node;
 
-		m_allocated++;
+		m_allocations++;
 		allocate_page_for_node_if_needed(node);
 		return address_of_node(node);
 	}
@@ -110,12 +109,13 @@ namespace Kernel
 	{
 		if (address % m_allocation_size)
 			return false;
+		if (m_allocations == 0)
+			return false;
 		
 		node* node = node_from_address(address);
 		if (node == nullptr)
 			return false;
 
-
 		if (!node->allocated)
 		{
 			dwarnln("deallocate called on unallocated address");
@@ -123,6 +123,8 @@ namespace Kernel
 		}
 		node->allocated = false;
 
+		if (node == m_used_list)
+			m_used_list = node->next;
 		if (node->prev)
 			node->prev->next = node->next;
 		if (node->next)
@@ -135,10 +137,15 @@ namespace Kernel
 			m_free_list->prev = node;
 		m_free_list = node;
 
-		m_allocated--;
+		m_allocations--;
 		return true;
 	}
 
+	uint32_t FixedWidthAllocator::max_allocations() const
+	{
+		return PAGE_SIZE / sizeof(node);
+	}
+
 	vaddr_t FixedWidthAllocator::address_of_node(const node* node) const
 	{
 		uint32_t index = node - (struct node*)m_nodes_page;

kernel/kernel/Process.cpp

@@ -105,11 +105,6 @@ namespace Kernel
 
 		delete elf;
 
-		MUST(process->m_fixed_width_allocators.emplace_back(process, 64));
-		MUST(process->m_fixed_width_allocators.emplace_back(process, 256));
-		MUST(process->m_fixed_width_allocators.emplace_back(process, 1024));
-		MUST(process->m_fixed_width_allocators.emplace_back(process, 4096));
-
 		register_process(process);
 		return process;
 	}
@@ -378,19 +373,55 @@ namespace Kernel
 		return {};
 	}
 
+	static constexpr uint16_t next_power_of_two(uint16_t value)
+	{
+		value--;
+		value |= value >> 1;
+		value |= value >> 2;
+		value |= value >> 4;
+		value |= value >> 8;
+		return value + 1;
+	}
+
 	BAN::ErrorOr<void*> Process::allocate(size_t bytes)
 	{
-		for (auto& allocator : m_fixed_width_allocators)
-			if (bytes <= allocator.allocation_size())
-				return (void*)allocator.allocate();
-		return BAN::Error::from_errno(ENOMEM);
+		if (bytes <= PAGE_SIZE)
+		{
+			// Do fixed width allocation
+			size_t allocation_size = next_power_of_two(bytes);
+			ASSERT(bytes <= allocation_size);
+
+			LockGuard _(m_lock);
+
+			for (auto& allocator : m_fixed_width_allocators)
+				if (allocator.allocation_size() == allocation_size && allocator.allocations() < allocator.max_allocations())
+					return (void*)allocator.allocate();
+
+			MUST(m_fixed_width_allocators.emplace_back(this, allocation_size));
+			return (void*)m_fixed_width_allocators.back().allocate();
+		}
+		else
+		{
+			// TODO: Do general allocation
+			return BAN::Error::from_errno(ENOMEM);
+		}
 	}
 
 	void Process::free(void* ptr)
 	{
-		for (auto& allocator : m_fixed_width_allocators)
-			if (allocator.deallocate((vaddr_t)ptr))
+		LockGuard _(m_lock);
+
+		for (auto it = m_fixed_width_allocators.begin(); it != m_fixed_width_allocators.end(); it++)
+		{
+			if (it->deallocate((vaddr_t)ptr))
+			{
+				// TODO: This might be too much. Maybe we should only
+				//       remove allocators when we have low memory... ?
+				if (it->allocations() == 0)
+					m_fixed_width_allocators.remove(it);
 				return;
+			}
+		}
 		dwarnln("free called on pointer that was not allocated");	
 	}
 

userspace/test.c

@@ -1,25 +1,34 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#define N 512
+
 int main()
 {
-	for (int i = 0; i < 10; i++)
+	for (int i = 0; i <= 10; i++)
 	{
-		int* ptrs[10];
-		for (int j = 0; j < 10; j++)
+		int** ptrs = malloc(N * sizeof(int*));
+		if (ptrs == NULL)
 		{
-			ptrs[j] = malloc(10);
+			perror("malloc");
+			return 1;
+		}
+		for (int j = 0; j < N; j++)
+		{
+			ptrs[j] = malloc(sizeof(int));
 			if (ptrs[j] == NULL)
 			{
 				perror("malloc");
 				return 1;
 			}
 			*ptrs[j] = j;
-			putc('0' + *ptrs[j], stdout);
+			putchar('0' + *ptrs[j] % 10);
 		}
-		for (int j = 0; j < 10; j++)
+		putchar('\n');
+
+		for (int j = 0; j < N; j++)
 			free(ptrs[j]);
-		putc('\n', stdout);
+		free(ptrs);
 	}
 	
 	return 0;