mm: add folios_put()

Patch series "Convert the swap code to be more folio-based".

There's still more to do with the swap code, but this reaps a lot of the
folio benefit.  More than 4kB of kernel text saved (with the UEK7 kernel
config).  I don't know how much that's going to translate into CPU
savings, but some of those compound_head() calls are on every page free,
so it should be noticable.  It might even be noticable just from an
I-cache consumption perspective.


This patch (of 22):

This is just a wrapper around release_pages() for now.  Place the
prototype in mm.h along with folio_put() and folio_put_refs().

Link: https://lkml.kernel.org/r/20220617175020.717127-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20220617175020.717127-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -1220,6 +1220,25 @@ static inline void folio_put_refs(struct folio *folio, int refs)
 		__put_page(&folio->page);
 }
 
+void release_pages(struct page **pages, int nr);
+
+/**
+ * folios_put - Decrement the reference count on an array of folios.
+ * @folios: The folios.
+ * @nr: How many folios there are.
+ *
+ * Like folio_put(), but for an array of folios.  This is more efficient
+ * than writing the loop yourself as it will optimise the locks which
+ * need to be taken if the folios are freed.
+ *
+ * Context: May be called in process or interrupt context, but not in NMI
+ * context.  May be called while holding a spinlock.
+ */
+static inline void folios_put(struct folio **folios, unsigned int nr)
+{
+	release_pages((struct page **)folios, nr);
+}
+
 static inline void put_page(struct page *page)
 {
 	struct folio *folio = page_folio(page);

include/linux/pagemap.h

@@ -345,8 +345,6 @@ static inline void filemap_nr_thps_dec(struct address_space *mapping)
 #endif
 }
 
-void release_pages(struct page **pages, int nr);
-
 struct address_space *page_mapping(struct page *);
 struct address_space *folio_mapping(struct folio *);
 struct address_space *swapcache_mapping(struct folio *);