[PATCH 30/35] mm: Implement find_get_entries_range()

[Jan Kara <jack@suse.cz>]

Implement a variant of find_get_entries() that stops iterating at
given index. Some callers want this, so let's provide the interface.
Also it makes the interface consistent with find_get_pages().

Signed-off-by: Jan Kara <jack@suse.cz>
---
 include/linux/pagemap.h | 13 ++++++++++---
 include/linux/pagevec.h | 12 ++++++++++--
 mm/filemap.c            | 32 ++++++++++++++++++++++++--------
 mm/swap.c               | 11 ++++++-----
 4 files changed, 50 insertions(+), 18 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 283d191c18be..df128a56f44b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -333,9 +333,16 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
 
 struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);
 struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset);
-unsigned find_get_entries(struct address_space *mapping, pgoff_t *start,
-			  unsigned int nr_entries, struct page **entries,
-			  pgoff_t *indices);
+unsigned find_get_entries_range(struct address_space *mapping, pgoff_t *start,
+			pgoff_t end, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices);
+static inline unsigned find_get_entries(struct address_space *mapping,
+			pgoff_t *start, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices)
+{
+	return find_get_entries_range(mapping, start, (pgoff_t)-1, nr_entries,
+				      entries, indices);
+}
 unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
 			pgoff_t end, unsigned int nr_pages,
 			struct page **pages);
diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
index 3798c142338d..93308689d6a7 100644
--- a/include/linux/pagevec.h
+++ b/include/linux/pagevec.h
@@ -22,10 +22,18 @@ struct pagevec {
 
 void __pagevec_release(struct pagevec *pvec);
 void __pagevec_lru_add(struct pagevec *pvec);
-unsigned pagevec_lookup_entries(struct pagevec *pvec,
+unsigned pagevec_lookup_entries_range(struct pagevec *pvec,
+				struct address_space *mapping,
+				pgoff_t *start, pgoff_t end,
+				unsigned nr_entries, pgoff_t *indices);
+static inline unsigned pagevec_lookup_entries(struct pagevec *pvec,
 				struct address_space *mapping,
 				pgoff_t *start, unsigned nr_entries,
-				pgoff_t *indices);
+				pgoff_t *indices)
+{
+	return pagevec_lookup_entries_range(pvec, mapping, start, (pgoff_t)-1,
+					    nr_entries, indices);
+}
 void pagevec_remove_exceptionals(struct pagevec *pvec);
 unsigned pagevec_lookup_range(struct pagevec *pvec,
 			      struct address_space *mapping,
diff --git a/mm/filemap.c b/mm/filemap.c
index de12b7355821..e55100459710 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1354,9 +1354,10 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
 EXPORT_SYMBOL(pagecache_get_page);
 
 /**
- * find_get_entries - gang pagecache lookup
+ * find_get_entries_range - gang pagecache lookup
  * @mapping:	The address_space to search
  * @start:	The starting page cache index
+ * @end:	The final page cache index (inclusive)
  * @nr_entries:	The maximum number of entries
  * @entries:	Where the resulting entries are placed
  * @indices:	The cache indices corresponding to the entries in @entries
@@ -1376,9 +1377,9 @@ EXPORT_SYMBOL(pagecache_get_page);
  * find_get_entries() returns the number of pages and shadow entries which were
  * found. It also updates @start to index the next page for the traversal.
  */
-unsigned find_get_entries(struct address_space *mapping,
-			  pgoff_t *start, unsigned int nr_entries,
-			  struct page **entries, pgoff_t *indices)
+unsigned find_get_entries_range(struct address_space *mapping,
+			pgoff_t *start, pgoff_t end, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices)
 {
 	void **slot;
 	unsigned int ret = 0;
@@ -1390,6 +1391,9 @@ unsigned find_get_entries(struct address_space *mapping,
 	rcu_read_lock();
 	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, *start) {
 		struct page *head, *page;
+
+		if (iter.index > end)
+			break;
 repeat:
 		page = radix_tree_deref_slot(slot);
 		if (unlikely(!page))
@@ -1425,13 +1429,25 @@ unsigned find_get_entries(struct address_space *mapping,
 export:
 		indices[ret] = iter.index;
 		entries[ret] = page;
-		if (++ret == nr_entries)
-			break;
+		if (++ret == nr_entries) {
+			*start = indices[ret - 1] + 1;
+			goto out;
+		}
 	}
+
+	/*
+	 * We come here when there is no page beyond @end. We take care to not
+	 * overflow the index @start as it confuses some of the callers. This
+	 * breaks the iteration when there is page at index -1 but that is
+	 * already broken anyway.
+	 */
+	if (end == (pgoff_t)-1)
+		*start = (pgoff_t)-1;
+	else
+		*start = end + 1;
+out:
 	rcu_read_unlock();
 
-	if (ret)
-		*start = indices[ret - 1] + 1;
 	return ret;
 }
 
diff --git a/mm/swap.c b/mm/swap.c
index 6ba3dab6e905..88c7eb4e97db 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -889,10 +889,11 @@ void __pagevec_lru_add(struct pagevec *pvec)
 EXPORT_SYMBOL(__pagevec_lru_add);
 
 /**
- * pagevec_lookup_entries - gang pagecache lookup
+ * pagevec_lookup_entries_range - gang pagecache lookup
  * @pvec:	Where the resulting entries are placed
  * @mapping:	The address_space to search
  * @start:	The starting entry index
+ * @end:	The final entry index (inclusive)
  * @nr_entries:	The maximum number of entries
  * @indices:	The cache indices corresponding to the entries in @pvec
  *
@@ -908,13 +909,13 @@ EXPORT_SYMBOL(__pagevec_lru_add);
  * pagevec_lookup_entries() returns the number of entries which were
  * found. It also updates @start to index the next page for the traversal.
  */
-unsigned pagevec_lookup_entries(struct pagevec *pvec,
+unsigned pagevec_lookup_entries_range(struct pagevec *pvec,
 				struct address_space *mapping,
-				pgoff_t *start, unsigned nr_pages,
+				pgoff_t *start, pgoff_t end, unsigned nr_pages,
 				pgoff_t *indices)
 {
-	pvec->nr = find_get_entries(mapping, start, nr_pages,
-				    pvec->pages, indices);
+	pvec->nr = find_get_entries_range(mapping, start, end, nr_pages,
+					  pvec->pages, indices);
 	return pagevec_count(pvec);
 }
 
-- 
2.12.3

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