Re: [PATCH V3 2/7] mm: move MADV_FREE pages into LRU_INACTIVE_FILE list

On Thu, Feb 16, 2017 at 12:52:53PM -0500, Johannes Weiner wrote:

On Tue, Feb 14, 2017 at 11:36:08AM -0800, Shaohua Li wrote:

quoted

@@ -126,4 +126,24 @@ static __always_inline enum lru_list page_lru(struct page *page)
 
 #define lru_to_page(head) (list_entry((head)->prev, struct page, lru))
 
+/*
+ * lazyfree pages are clean anonymous pages. They have SwapBacked flag cleared
+ * to destinguish normal anonymous pages.
+ */
+static inline void set_page_lazyfree(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageAnon(page) || !PageSwapBacked(page), page);
+	ClearPageSwapBacked(page);
+}
+
+static inline void clear_page_lazyfree(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageAnon(page) || PageSwapBacked(page), page);
+	SetPageSwapBacked(page);
+}
+
+static inline bool page_is_lazyfree(struct page *page)
+{
+	return PageAnon(page) && !PageSwapBacked(page);
+}

Sorry for not getting to v2 in time, but I have to say I strongly
agree with your first iterations and would much prefer this to be
open-coded.

IMO this needlessly introduces a new state opaquely called "lazyfree",
when really that's just anonymous pages that don't need to be swapped
before reclaim - PageAnon && !PageSwapBacked. Very simple MM concept.

That especially shows when we later combine it with page_is_file_cache
checks like the next patch does.

The rest of the patch looks good to me.

Thanks! I do agree checking PageSwapBacked is clearer, but Minchan convinced me
because of the accounting issue. Where do you suggest we should put the
accounting to?

Thanks,
Shaohua

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