SImplify init_physical_frame_allocator() even more

kernel/src/memory/MemoryManager.cpp

@@ -54,29 +54,26 @@ namespace MemoryManager
 
     void init_physical_frame_allocator()
     {
-        u64 total_mem = 0;
-
         MemoryMapIterator iter;
-
         MemoryMapEntry entry;
-        while (iter.next().try_set_value(entry)) { total_mem += entry.size; }
 
         auto largest_free = iter.largest_free();
 
-        void* biggest_usable_memory_block = (void*)largest_free.ptr;
-        u64 biggest_usable_memory_block_size = largest_free.size;
+        expect(largest_free.free, "We were given a largest free block that isn't even free!");
 
         // The entire physical address space. May contain inexistent memory holes, thus differs from total_mem which
         // only counts existent memory. Our bitmap needs to have space for all of the physical address space, since
         // usable addresses will be scattered across it.
         usize physical_address_space_size = get_physical_address_space_size();
 
-        char* frame_bitmap_addr = (char*)biggest_usable_memory_block;
+        // We store our frame bitmap at the beginning of the largest free memory block.
+        char* frame_bitmap_addr = (char*)largest_free.ptr;
+
         usize frame_bitmap_size = physical_address_space_size / ARCH_PAGE_SIZE / 8 + 1;
 
         // This should never happen, unless memory is very fragmented. Usually there is always a very big block of
         // usable memory and then some tiny blocks around it.
-        if (frame_bitmap_size >= biggest_usable_memory_block_size) [[unlikely]]
+        if (frame_bitmap_size >= largest_free.size) [[unlikely]]
         {
             kerrorln("ERROR: No single memory block is enough to hold the frame bitmap");
             CPU::efficient_halt();