mm: add find_lock_head

Add a new FGP_HEAD flag which avoids calling find_subpage() and add a
convenience wrapper for it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Link: https://lkml.kernel.org/r/20200910183318.20139-9-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 26 insertions, 6 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 5176009e4ffa..1a3554f5d992 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -279,6 +279,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
 #define FGP_NOFS		0x00000010
 #define FGP_NOWAIT		0x00000020
 #define FGP_FOR_MMAP		0x00000040
+#define FGP_HEAD		0x00000080
 
 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
 		int fgp_flags, gfp_t cache_gfp_mask);
@@ -310,18 +311,37 @@ static inline struct page *find_get_page_flags(struct address_space *mapping,
  * @mapping: the address_space to search
  * @offset: the page index
  *
- * Looks up the page cache slot at @mapping & @offset.  If there is a
+ * Looks up the page cache entry at @mapping & @offset.  If there is a
  * page cache page, it is returned locked and with an increased
  * refcount.
  *
- * Otherwise, %NULL is returned.
- *
- * find_lock_page() may sleep.
+ * Context: May sleep.
+ * Return: A struct page or %NULL if there is no page in the cache for this
+ * index.
  */
 static inline struct page *find_lock_page(struct address_space *mapping,
-					pgoff_t offset)
+					pgoff_t index)
+{
+	return pagecache_get_page(mapping, index, FGP_LOCK, 0);
+}
+
+/**
+ * find_lock_head - Locate, pin and lock a pagecache page.
+ * @mapping: The address_space to search.
+ * @offset: The page index.
+ *
+ * Looks up the page cache entry at @mapping & @offset.  If there is a
+ * page cache page, its head page is returned locked and with an increased
+ * refcount.
+ *
+ * Context: May sleep.
+ * Return: A struct page which is !PageTail, or %NULL if there is no page
+ * in the cache for this index.
+ */
+static inline struct page *find_lock_head(struct address_space *mapping,
+					pgoff_t index)
 {
-	return pagecache_get_page(mapping, offset, FGP_LOCK, 0);
+	return pagecache_get_page(mapping, index, FGP_LOCK | FGP_HEAD, 0);
 }
 
 /**