From e312fbdbd6cd39ee9b77d5f90774d6b83100bf9b Mon Sep 17 00:00:00 2001
From: 423A35C7 <609514299@qq.com>
Date: Tue, 7 May 2024 21:50:16 +0800
Subject: [PATCH] =?UTF-8?q?=E5=AE=8C=E6=88=90=E5=AE=9E=E9=AA=8C3?=
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实现第二次机会页面置换算法
---
 labcodes_answer/lab3_result/kern/mm/swap_fifo.c | 32 +++++++++++++++++++------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/labcodes_answer/lab3_result/kern/mm/swap_fifo.c b/labcodes_answer/lab3_result/kern/mm/swap_fifo.c
index 4f9dc8f..3c231b1 100644
--- a/labcodes_answer/lab3_result/kern/mm/swap_fifo.c
+++ b/labcodes_answer/lab3_result/kern/mm/swap_fifo.c
@@ -69,7 +69,25 @@ _fifo_swap_out_victim(struct mm_struct *mm, struct Page ** ptr_page, int in_tick
      //(1)  unlink the  earliest arrival page in front of pra_list_head qeueue
      //(2)  set the addr of addr of this page to ptr_page
      /* Select the tail */
-     list_entry_t *le = head->prev;
+    //  从后往前，最后面的是最早访问的
+     list_entry_t *current = head->prev;
+     list_entry_t *le = NULL;
+     for (; current != head; current = current->prev) {
+        pte_t *ptep = get_pte(mm->pgdir, le2vma(current, vm_start), 0);
+        cprintf("@@@ %d %x :a page\n", *ptep & PTE_A, current);
+        if (*ptep & PTE_A) { // 访问位为1
+            *ptep &= !PTE_A; // 清除访问位
+            list_del(current); // 从链表中移除
+            list_add(head, current); // 添加到链表头部
+            cprintf("### %d %x :clear access\n", *ptep & PTE_A, current);
+        } else {
+            le = current;
+            break;
+        }
+     }
+     if (le == NULL) {
+        le = head->prev; // 循环一遍找不到就最后一个
+     }
      assert(head!=le);
      struct Page *p = le2page(le, pra_page_link);
      list_del(le);
@@ -97,26 +115,26 @@ _fifo_check_swap(void) {
     assert(pgfault_num==5);
     cprintf("write Virt Page b in fifo_check_swap\n");
     *(unsigned char *)0x2000 = 0x0b;
-    assert(pgfault_num==5);
+    assert(pgfault_num==6); // 从这里开始缺页次数与FIFO不同了
     cprintf("write Virt Page a in fifo_check_swap\n");
     *(unsigned char *)0x1000 = 0x0a;
     assert(pgfault_num==6);
     cprintf("write Virt Page b in fifo_check_swap\n");
     *(unsigned char *)0x2000 = 0x0b;
-    assert(pgfault_num==7);
+    assert(pgfault_num==6);
     cprintf("write Virt Page c in fifo_check_swap\n");
     *(unsigned char *)0x3000 = 0x0c;
-    assert(pgfault_num==8);
+    assert(pgfault_num==7);
     cprintf("write Virt Page d in fifo_check_swap\n");
     *(unsigned char *)0x4000 = 0x0d;
-    assert(pgfault_num==9);
+    assert(pgfault_num==8);
     cprintf("write Virt Page e in fifo_check_swap\n");
     *(unsigned char *)0x5000 = 0x0e;
-    assert(pgfault_num==10);
+    assert(pgfault_num==8);
     cprintf("write Virt Page a in fifo_check_swap\n");
     assert(*(unsigned char *)0x1000 == 0x0a);
     *(unsigned char *)0x1000 = 0x0a;
-    assert(pgfault_num==11);
+    assert(pgfault_num==9);
     return 0;
 }