[PATCH v5 2/3] mm: filemap: introduce mark_page_usedonce

[Andrea Righi <andrea@betterlinux.com>]

Introduce a helper function to drop a page from the page cache if it is
evictable, inactive and unreferenced.

This can be used to drop used-once pages from the file cache with
POSIX_FADV_NOREUSE.

Signed-off-by: Andrea Righi <andrea@betterlinux.com>
---
 include/linux/swap.h |    1 +
 mm/swap.c            |   24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 3e60228..2e5d1b8 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -222,6 +222,7 @@ extern void lru_add_page_tail(struct zone* zone,
 			      struct page *page, struct page *page_tail);
 extern void activate_page(struct page *);
 extern void mark_page_accessed(struct page *);
+extern void mark_page_usedonce(struct page *page);
 extern void lru_add_drain(void);
 extern int lru_add_drain_all(void);
 extern void rotate_reclaimable_page(struct page *page);
diff --git a/mm/swap.c b/mm/swap.c
index fff1ff7..2c19c92 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -352,6 +352,30 @@ void activate_page(struct page *page)
 }
 #endif
 
+/**
+ * mark_page_usedonce - handle used-once pages
+ * @page: the page set as used-once
+ *
+ * Drop a page from the page cache if it is evictable, inactive and
+ * unreferenced.
+ */
+void mark_page_usedonce(struct page *page)
+{
+	int ret;
+
+	if (!PageLRU(page))
+		return;
+	if (PageActive(page) || PageUnevictable(page) || PageReferenced(page))
+		return;
+	if (lock_page_killable(page))
+		return;
+	ret = invalidate_inode_page(page);
+	unlock_page(page);
+	if (!ret)
+		deactivate_page(page);
+}
+EXPORT_SYMBOL(mark_page_usedonce);
+
 /*
  * Mark a page as having seen activity.
  *
-- 
1.7.5.4

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