[PATCH/RFC v2 2/3] mm/swap: introduce free_pages_and_swap_cache_nolru()

[Nikita Yushchenko <nikita.yushchenko@xxxxxxxxxxxxx>]

This is a variant of free_pages_and_swap_cache() that does not call
lru_add_drain(), for better performance in case when the passed pages
are guaranteed to not be in LRU.

Signed-off-by: Nikita Yushchenko <nikita.yushchenko@xxxxxxxxxxxxx>
---
 include/linux/swap.h |  5 ++++-
 mm/swap_state.c      | 29 ++++++++++++++++++++++-------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index d1ea44b31f19..86a1b0a61889 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -460,6 +460,7 @@ extern void clear_shadow_from_swap_cache(int type, unsigned long begin,
 extern void free_swap_cache(struct page *);
 extern void free_page_and_swap_cache(struct page *);
 extern void free_pages_and_swap_cache(struct page **, int);
+extern void free_pages_and_swap_cache_nolru(struct page **, int);
 extern struct page *lookup_swap_cache(swp_entry_t entry,
 				      struct vm_area_struct *vma,
 				      unsigned long addr);
@@ -565,7 +566,9 @@ static inline struct address_space *swap_address_space(swp_entry_t entry)
 #define free_page_and_swap_cache(page) \
 	put_page(page)
 #define free_pages_and_swap_cache(pages, nr) \
-	release_pages((pages), (nr));
+	release_pages((pages), (nr))
+#define free_pages_and_swap_cache_nolru(pages, nr) \
+	release_pages((pages), (nr))
 
 static inline void free_swap_cache(struct page *page)
 {
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 8d4104242100..a5d9fd258f0a 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -307,17 +307,32 @@ void free_page_and_swap_cache(struct page *page)
 
 /*
  * Passed an array of pages, drop them all from swapcache and then release
- * them.  They are removed from the LRU and freed if this is their last use.
+ * them.  They are optionally removed from the LRU and freed if this is their
+ * last use.
  */
-void free_pages_and_swap_cache(struct page **pages, int nr)
+static void __free_pages_and_swap_cache(struct page **pages, int nr,
+		bool do_lru)
 {
-	struct page **pagep = pages;
 	int i;
 
-	lru_add_drain();
-	for (i = 0; i < nr; i++)
-		free_swap_cache(pagep[i]);
-	release_pages(pagep, nr);
+	if (do_lru)
+		lru_add_drain();
+	for (i = 0; i < nr; i++) {
+		if (!do_lru)
+			VM_WARN_ON_ONCE_PAGE(PageLRU(pages[i]), pages[i]);
+		free_swap_cache(pages[i]);
+	}
+	release_pages(pages, nr);
+}
+
+void free_pages_and_swap_cache(struct page **pages, int nr)
+{
+	__free_pages_and_swap_cache(pages, nr, true);
+}
+
+void free_pages_and_swap_cache_nolru(struct page **pages, int nr)
+{
+	__free_pages_and_swap_cache(pages, nr, false);
 }
 
 static inline bool swap_use_vma_readahead(void)
-- 
2.30.2