Step 3 - TLB（全相联 + LRU）

Assets/Scripts/Simulation/TlbCache.cs

@@ -0,0 +1,121 @@
+using System;
+using System.Collections.Generic;
+
+namespace VMdemo.Simulation
+{
+    public class TlbCache
+    {
+        private readonly Dictionary<ulong, LinkedListNode<TlbEntry>> _index;
+        private readonly LinkedList<TlbEntry> _lruList;
+
+        public TlbCache(int capacity)
+        {
+            if (capacity <= 0)
+            {
+                throw new ArgumentOutOfRangeException(nameof(capacity), "TLB 容量必须是正整数。");
+            }
+
+            Capacity = capacity;
+            _index = new Dictionary<ulong, LinkedListNode<TlbEntry>>(capacity);
+            _lruList = new LinkedList<TlbEntry>();
+        }
+
+        public int Capacity { get; }
+        public int Count => _index.Count;
+        public int HitCount { get; private set; }
+        public int MissCount { get; private set; }
+
+        public bool Lookup(ulong vpn, out ulong pfn)
+        {
+            return TryLookup(vpn, out pfn);
+        }
+
+        public bool TryLookup(ulong vpn, out ulong pfn)
+        {
+            if (_index.TryGetValue(vpn, out var node) && node.Value.IsValid)
+            {
+                MoveToMostRecent(node);
+                pfn = node.Value.Pfn;
+                HitCount++;
+                return true;
+            }
+
+            pfn = 0UL;
+            MissCount++;
+            return false;
+        }
+
+        public void InsertOrUpdate(ulong vpn, ulong pfn)
+        {
+            if (_index.TryGetValue(vpn, out var existingNode))
+            {
+                existingNode.Value = existingNode.Value.WithPfn(pfn);
+                MoveToMostRecent(existingNode);
+                return;
+            }
+
+            var newNode = new LinkedListNode<TlbEntry>(new TlbEntry(vpn, pfn));
+            _lruList.AddFirst(newNode);
+            _index[vpn] = newNode;
+
+            if (_index.Count > Capacity)
+            {
+                EvictLeastRecent();
+            }
+        }
+
+        public bool Remove(ulong vpn)
+        {
+            if (!_index.TryGetValue(vpn, out var node))
+            {
+                return false;
+            }
+
+            _lruList.Remove(node);
+            _index.Remove(vpn);
+            return true;
+        }
+
+        public void Clear()
+        {
+            _lruList.Clear();
+            _index.Clear();
+            HitCount = 0;
+            MissCount = 0;
+        }
+
+        public IReadOnlyList<TlbEntry> GetEntriesMostRecentFirst()
+        {
+            var snapshot = new List<TlbEntry>(_index.Count);
+            for (var node = _lruList.First; node != null; node = node.Next)
+            {
+                snapshot.Add(node.Value);
+            }
+
+            return snapshot;
+        }
+
+        private void MoveToMostRecent(LinkedListNode<TlbEntry> node)
+        {
+            if (node.List != _lruList || _lruList.First == node)
+            {
+                return;
+            }
+
+            _lruList.Remove(node);
+            _lruList.AddFirst(node);
+        }
+
+        private void EvictLeastRecent()
+        {
+            var leastRecentNode = _lruList.Last;
+            if (leastRecentNode == null)
+            {
+                return;
+            }
+
+            _lruList.RemoveLast();
+            _index.Remove(leastRecentNode.Value.Vpn);
+        }
+    }
+}

Assets/Scripts/Simulation/TlbCache.cs.meta

@@ -0,0 +1,11 @@
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Assets/Scripts/Simulation/TlbEntry.cs

@@ -0,0 +1,29 @@
+using System;
+
+namespace VMdemo.Simulation
+{
+    [Serializable]
+    public readonly struct TlbEntry
+    {
+        public TlbEntry(ulong vpn, ulong pfn, bool isValid = true)
+        {
+            Vpn = vpn;
+            Pfn = pfn;
+            IsValid = isValid;
+        }
+
+        public ulong Vpn { get; }
+        public ulong Pfn { get; }
+        public bool IsValid { get; }
+
+        public TlbEntry WithPfn(ulong pfn)
+        {
+            return new TlbEntry(Vpn, pfn, true);
+        }
+
+        public override string ToString()
+        {
+            return $"VPN={Vpn}, PFN={Pfn}, Valid={IsValid}";
+        }
+    }
+}

Assets/Scripts/Simulation/TlbEntry.cs.meta

@@ -0,0 +1,11 @@
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Assets/Tests/EditMode/Step3TlbCacheTests.cs

@@ -0,0 +1,130 @@
+using NUnit.Framework;
+using VMdemo.Simulation;
+
+namespace VMdemo.Tests.EditMode
+{
+    public class Step3TlbCacheTests
+    {
+        [Test]
+        public void Constructor_CapacityLessThanOne_Throws()
+        {
+            Assert.Throws<System.ArgumentOutOfRangeException>(() => new TlbCache(0));
+            Assert.Throws<System.ArgumentOutOfRangeException>(() => new TlbCache(-1));
+        }
+
+        [Test]
+        public void TryLookup_Miss_ReturnsFalseAndCountsMiss()
+        {
+            var cache = new TlbCache(2);
+
+            var hit = cache.TryLookup(10UL, out var pfn);
+
+            Assert.IsFalse(hit);
+            Assert.That(pfn, Is.EqualTo(0UL));
+            Assert.That(cache.HitCount, Is.EqualTo(0));
+            Assert.That(cache.MissCount, Is.EqualTo(1));
+        }
+
+        [Test]
+        public void InsertOrUpdate_AndLookup_HitReturnsMappedPfn()
+        {
+            var cache = new TlbCache(2);
+            cache.InsertOrUpdate(10UL, 100UL);
+
+            var hit = cache.TryLookup(10UL, out var pfn);
+
+            Assert.IsTrue(hit);
+            Assert.That(pfn, Is.EqualTo(100UL));
+            Assert.That(cache.HitCount, Is.EqualTo(1));
+            Assert.That(cache.MissCount, Is.EqualTo(0));
+        }
+
+        [Test]
+        public void InsertOrUpdate_ExistingEntry_UpdatesPfnAndMovesToMostRecent()
+        {
+            var cache = new TlbCache(3);
+            cache.InsertOrUpdate(1UL, 11UL);
+            cache.InsertOrUpdate(2UL, 22UL);
+            cache.InsertOrUpdate(3UL, 33UL);
+
+            cache.InsertOrUpdate(1UL, 111UL);
+
+            var entries = cache.GetEntriesMostRecentFirst();
+
+            Assert.That(entries.Count, Is.EqualTo(3));
+            Assert.That(entries[0].Vpn, Is.EqualTo(1UL));
+            Assert.That(entries[0].Pfn, Is.EqualTo(111UL));
+            Assert.That(entries[1].Vpn, Is.EqualTo(3UL));
+            Assert.That(entries[2].Vpn, Is.EqualTo(2UL));
+        }
+
+        [Test]
+        public void OverCapacity_EvictsLeastRecentlyUsedEntry()
+        {
+            var cache = new TlbCache(3);
+            cache.InsertOrUpdate(1UL, 11UL);
+            cache.InsertOrUpdate(2UL, 22UL);
+            cache.InsertOrUpdate(3UL, 33UL);
+
+            cache.TryLookup(1UL, out _); // refresh 1 as MRU
+            cache.InsertOrUpdate(4UL, 44UL); // should evict 2
+
+            Assert.That(cache.Count, Is.EqualTo(3));
+            Assert.IsFalse(cache.TryLookup(2UL, out _));
+            Assert.IsTrue(cache.TryLookup(1UL, out var pfn1));
+            Assert.That(pfn1, Is.EqualTo(11UL));
+
+            var entries = cache.GetEntriesMostRecentFirst();
+            Assert.That(entries[0].Vpn, Is.EqualTo(1UL));
+            Assert.That(entries[1].Vpn, Is.EqualTo(4UL));
+            Assert.That(entries[2].Vpn, Is.EqualTo(3UL));
+        }
+
+        [Test]
+        public void Remove_ExistingAndMissingKeys_BehaveAsExpected()
+        {
+            var cache = new TlbCache(2);
+            cache.InsertOrUpdate(5UL, 55UL);
+
+            var removedFirst = cache.Remove(5UL);
+            var removedSecond = cache.Remove(5UL);
+
+            Assert.IsTrue(removedFirst);
+            Assert.IsFalse(removedSecond);
+            Assert.That(cache.Count, Is.EqualTo(0));
+        }
+
+        [Test]
+        public void Clear_ResetsEntriesAndCounters()
+        {
+            var cache = new TlbCache(2);
+            cache.InsertOrUpdate(1UL, 10UL);
+            cache.InsertOrUpdate(2UL, 20UL);
+            cache.TryLookup(1UL, out _);
+            cache.TryLookup(99UL, out _);
+
+            cache.Clear();
+
+            Assert.That(cache.Count, Is.EqualTo(0));
+            Assert.That(cache.HitCount, Is.EqualTo(0));
+            Assert.That(cache.MissCount, Is.EqualTo(0));
+            Assert.That(cache.GetEntriesMostRecentFirst().Count, Is.EqualTo(0));
+        }
+
+        [Test]
+        public void ContinuousLookup_TracksHitAndMissCountsAccurately()
+        {
+            var cache = new TlbCache(2);
+            cache.InsertOrUpdate(1UL, 10UL);
+            cache.InsertOrUpdate(2UL, 20UL);
+
+            cache.TryLookup(1UL, out _);   // hit
+            cache.TryLookup(3UL, out _);   // miss
+            cache.TryLookup(2UL, out _);   // hit
+            cache.TryLookup(3UL, out _);   // miss
+
+            Assert.That(cache.HitCount, Is.EqualTo(2));
+            Assert.That(cache.MissCount, Is.EqualTo(2));
+        }
+    }
+}

Assets/Tests/EditMode/Step3TlbCacheTests.cs.meta

@@ -0,0 +1,11 @@
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doc/MVP-TODO.md

@@ -83,20 +83,20 @@
 
 ### TODO
 
-- [ ] 新建 `TlbEntry.cs`：`VPN -> PFN` 映射及有效位
-- [ ] 新建 `TlbCache.cs`：查询、更新、淘汰
-- [ ] 使用 `Dictionary + LinkedList` 实现 O(1) 级 LRU
+- [x] 新建 `TlbEntry.cs`：`VPN -> PFN` 映射及有效位
+- [x] 新建 `TlbCache.cs`：查询、更新、淘汰
+- [x] 使用 `Dictionary + LinkedList` 实现 O(1) 级 LRU
 
 ### 行为要求
 
-- [ ] `Lookup(vpn)`：命中返回 PFN，未命中返回失败
-- [ ] `InsertOrUpdate(vpn, pfn)`：已存在则更新并置为最近使用
-- [ ] 超出容量时淘汰最久未使用项
+- [x] `Lookup(vpn)`：命中返回 PFN，未命中返回失败
+- [x] `InsertOrUpdate(vpn, pfn)`：已存在则更新并置为最近使用
+- [x] 超出容量时淘汰最久未使用项
 
 ### 完成标准
 
-- [ ] 构造用例可验证 LRU 淘汰顺序正确
-- [ ] 连续访问时命中统计准确
+- [x] 构造用例可验证 LRU 淘汰顺序正确
+- [x] 连续访问时命中统计准确
 
 ## 5. Step 4 - 二级页表 + 缺页 + FIFO
 
@@ -207,4 +207,4 @@
 
 - [x] 先完成 Step 1（参数模型 + 校验）
 - [x] 紧接 Step 2（地址拆分）
-- [ ] 当天收尾前完成 Step 3（TLB LRU 最小可运行）
+- [x] 当天收尾前完成 Step 3（TLB LRU 最小可运行）