将虚拟文件系统和使用lru算法模拟分页式虚拟内存相结合的python代码，其中 虚拟内存1M，文件系统中创建的文件要在虚拟内存中占一定大小

以下是一个简单的示例代码，它结合了虚拟文件系统和使用LRU算法模拟分页式虚拟内存：

import os
from collections import OrderedDict

VIRTUAL_MEMORY_SIZE = 1024 * 1024  # 1M
PAGE_SIZE = 4 * 1024  # 4KB
NUM_PAGES = VIRTUAL_MEMORY_SIZE // PAGE_SIZE
NUM_FRAMES = 256  # number of frames in physical memory
FRAME_SIZE = PAGE_SIZE  # frame size equals page size

# Define a simple virtual file system
class VirtualFileSystem:
    def __init__(self):
        self.files = {}

    def create_file(self, file_name, size):
        self.files[file_name] = bytearray(size)

    def write_file(self, file_name, offset, data):
        for i, byte in enumerate(data):
            self.files[file_name][offset + i] = byte

    def read_file(self, file_name, offset, size):
        return self.files[file_name][offset:offset+size]

# Define a simple LRU cache
class LRUCache:
    def __init__(self, max_size):
        self.max_size = max_size
        self.cache = OrderedDict()

    def get(self, key):
        if key not in self.cache:
            return None
        value = self.cache.pop(key)
        self.cache[key] = value
        return value

    def put(self, key, value):
        if key in self.cache:
            self.cache.pop(key)
        elif len(self.cache) >= self.max_size:
            self.cache.popitem(last=False)
        self.cache[key] = value

# Define a simple virtual memory
class VirtualMemory:
    def __init__(self):
        self.page_table = {}
        self.physical_memory = bytearray(NUM_FRAMES * FRAME_SIZE)
        self.cache = LRUCache(max_size=NUM_FRAMES)

    def read_byte(self, virtual_address):
        page_num, offset = divmod(virtual_address, PAGE_SIZE)

        # Check if page is in page table
        if page_num not in self.page_table:
            # Page fault, load page from disk
            self.load_page_from_disk(page_num)

        # Translate virtual address to physical address
        frame_num = self.page_table[page_num]
        physical_address = frame_num * FRAME_SIZE + offset

        # Check if frame is in cache
        frame_data = self.cache.get(frame_num)
        if frame_data is None:
            # Read frame from physical memory
            frame_data = self.physical_memory[physical_address:physical_address+FRAME_SIZE]
            # Add frame to cache
            self.cache.put(frame_num, frame_data)

        # Return byte at physical address
        return frame_data[offset]

    def load_page_from_disk(self, page_num):
        # Load page from virtual file system
        data = vfs.read_file('page_{}'.format(page_num), 0, PAGE_SIZE)
        # Find a free frame in physical memory
        frame_num = self.find_free_frame()
        # Write page to physical memory
        self.write_frame_to_memory(frame_num, data)
        # Update page table
        self.page_table[page_num] = frame_num

    def find_free_frame(self):
        # Find a free frame in physical memory (using LRU algorithm)
        for i in range(NUM_FRAMES):
            if i not in self.page_table.values():
                return i
        # No free frames available, evict least recently used frame
        evicted_frame_num = list(self.cache.cache.keys())[0]
        self.evict_frame(evicted_frame_num)
        return evicted_frame_num

    def write_frame_to_memory(self, frame_num, data):
        # Write data to physical memory at specified frame
        offset = frame_num * FRAME_SIZE
        self.physical_memory[offset:offset+FRAME_SIZE] = data

    def evict_frame(self, frame_num):
        # Evict least recently used frame from cache and write to disk
        page_num_to_evict = None
        for page_num, frame in self.page_table.items():
            if frame == frame_num:
                page_num_to_evict = page_num
                break
        if page_num_to_evict is not None:
            # Write frame to virtual file system
            data = self.physical_memory[frame_num * FRAME_SIZE:(frame_num+1) * FRAME_SIZE]
            vfs.write_file('page_{}'.format(page_num_to_evict), 0, data)
            # Remove page from page table
            del self.page_table[page_num_to_evict]
        # Remove frame from cache
        self.cache.cache.pop(frame_num, None)

# Test the virtual memory
vfs = VirtualFileSystem()
vfs.create_file('file1', PAGE_SIZE * 2)
vfs.write_file('file1', 0, b'hello world')
vfs.write_file('file1', PAGE_SIZE, b'foo bar')

vm = VirtualMemory()
assert vm.read_byte(0) == b'h'
assert vm.read_byte(PAGE_SIZE + 3) == b'b'
assert vm.read_byte(PAGE_SIZE * 2 + 3) == None  # page fault
assert vm.read_byte(PAGE_SIZE * 2) == b'h'  # page loaded from disk
assert vm.read_byte(PAGE_SIZE * 2 + PAGE_SIZE) == None  # page fault
assert vm.read_byte(PAGE_SIZE * 2 + PAGE_SIZE + 3) == b'b'  # page loaded from disk