[PATCH 3/4] pagevec: Add dynamically allocated pagevecs

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

Add pagevec_alloc() and pagevec_free() to allow for pagevecs up to 255
entries in size.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/pagevec.h |  7 +++++++
 mm/swap.c               | 28 ++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
index 4dc45392d776..4d5a48d7a372 100644
--- a/include/linux/pagevec.h
+++ b/include/linux/pagevec.h
@@ -36,6 +36,13 @@ struct pagevec {
 
 void __pagevec_release(struct pagevec *pvec);
 void __pagevec_lru_add(struct pagevec *pvec);
+struct pagevec *pagevec_alloc(unsigned long sz, gfp_t gfp);
+
+static inline void pagevec_free(struct pagevec *pvec)
+{
+	kfree(pvec);
+}
+
 void pagevec_remove_exceptionals(struct pagevec *pvec);
 
 unsigned pagevec_lookup_range_tag(struct pagevec *pvec,
diff --git a/mm/swap.c b/mm/swap.c
index 1e6f50b312ea..3f856a272cb2 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -988,6 +988,34 @@ void __pagevec_release(struct pagevec *pvec)
 }
 EXPORT_SYMBOL(__pagevec_release);
 
+/**
+ * pagevec_alloc - Allocate a pagevec.
+ * @sz: Number of pages wanted.
+ * @gfp: Memory allocation flags.
+ *
+ * Allocates a new pagevec.  The @sz parameter is advisory; this function
+ * may allocate a pagevec that can contain fewer pages than requested.  If
+ * the caller cares how many were allocated, it can check pagevec_size(),
+ * but most callers will simply use as many as were allocated.
+ *
+ * Return: A new pagevec, or NULL if memory allocation failed.
+ */
+struct pagevec *pagevec_alloc(unsigned long sz, gfp_t gfp)
+{
+	struct pagevec *pvec;
+
+	if (sz > 255)
+		sz = 255;
+	pvec = kmalloc_array(sz + 1, sizeof(void *), gfp);
+	if (!pvec)
+		return NULL;
+	pvec->nr = 0;
+	pvec->sz = sz;
+
+	return pvec;
+}
+EXPORT_SYMBOL(pagevec_alloc);
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 /* used by __split_huge_page_refcount() */
 void lru_add_page_tail(struct page *page, struct page *page_tail,
-- 
2.28.0