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標題: anon page到inactive lru之后還能回active lru嗎？page_check_references()問題。 [打印本頁]

作者: blake326 時間: 2015-10-21 10:28
標題: anon page到inactive lru之后還能回active lru嗎？page_check_references()問題。
畫了一個anon page life的狀態(tài)圖。

發(fā)現(xiàn)點疑問，當page到inactive lru時，此時應(yīng)用再訪問它的話，則會缺頁異常激活young pte, 考慮現(xiàn)在只有一個young pte的話，page_check_references代碼看起來只會keep在inactive lru中。不知道是否分析正確？

static enum page_references page_check_references(struct page *page,
   struct scan_control *sc)
{
int referenced_ptes, referenced_page;
unsigned long vm_flags;

referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
   &vm_flags);
referenced_page = TestClearPageReferenced(page);

/*
   * Mlock lost the isolation race with us.  Let try_to_unmap()
   * move the page to the unevictable list.
   */
if (vm_flags & VM_LOCKED)
return PAGEREF_RECLAIM;

if (referenced_ptes) {
if (PageSwapBacked(page))
return PAGEREF_ACTIVATE;
/*
   * All mapped pages start out with page table
   * references from the instantiating fault, so we need
   * to look twice if a mapped file page is used more
   * than once.
   *
   * Mark it and spare it for another trip around the
   * inactive list.  Another page table reference will
   * lead to its activation.
   *
   * Note: the mark is set for activated pages as well
   * so that recently deactivated but used pages are
   * quickly recovered.
   */
SetPageReferenced(page);

if (referenced_page || referenced_ptes > 1)
return PAGEREF_ACTIVATE;

/*
   * Activate file-backed executable pages after first usage.
   */
if (vm_flags & VM_EXEC)
return PAGEREF_ACTIVATE;

return PAGEREF_KEEP;
}

/* Reclaim if clean, defer dirty pages to writeback */
if (referenced_page && !PageSwapBacked(page))
return PAGEREF_RECLAIM_CLEAN;

return PAGEREF_RECLAIM;
}

作者: blake326 時間: 2015-10-21 10:56
SetPageReferenced(page);

if (referenced_page || referenced_ptes > 1)
return PAGEREF_ACTIVATE;

判斷referenced_ptes > 1還有一個refrence_page條件。那么看起來流程是這樣的：

1. new page， active anon lru
2. shrink_active_list, (old lpte, no hw pte), inactive anon lru
3. 用戶訪問缺頁異常。 (young lpte, hw pte), inactive anon lru
4. shrink_inactive_list, keep inactive anon lru (set page referenced)(old lpte, no hw pte)
5. 用戶訪問缺頁異常。(young lpte, hw pte), inactive anon lru， page referenced
6. shrink_inactive_list, because page referenced and young pte, 回active anon lru

不知理解是否正確。

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