filemap: Add filemap_get_folios()

This is the equivalent of find_get_pages() but fills a folio_batch
instead of an array of pages.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index dee519ef7436e22d5b15ec1d431785144b6a4095..cfd0e8001b3b38af378926ebef03dc1d1ca1235b 100644 (file)
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -718,6 +718,8 @@ static inline struct page *find_subpage(struct page *head, pgoff_t index)
        return head + (index & (thp_nr_pages(head) - 1));
 }
 
+unsigned filemap_get_folios(struct address_space *mapping, pgoff_t *start,
+               pgoff_t end, struct folio_batch *fbatch);
 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/mm/filemap.c b/mm/filemap.c
index 22a17ab256f7677bc193cb9a79a72e7ea472854e..ce3209a8ad49e476376f8e035510c6247bb33e26 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2127,6 +2127,65 @@ put:
        return folio_batch_count(fbatch);
 }
 
+/**
+ * filemap_get_folios - Get a batch of folios
+ * @mapping:   The address_space to search
+ * @start:     The starting page index
+ * @end:       The final page index (inclusive)
+ * @fbatch:    The batch to fill.
+ *
+ * Search for and return a batch of folios in the mapping starting at
+ * index @start and up to index @end (inclusive).  The folios are returned
+ * in @fbatch with an elevated reference count.
+ *
+ * The first folio may start before @start; if it does, it will contain
+ * @start.  The final folio may extend beyond @end; if it does, it will
+ * contain @end.  The folios have ascending indices.  There may be gaps
+ * between the folios if there are indices which have no folio in the
+ * page cache.  If folios are added to or removed from the page cache
+ * while this is running, they may or may not be found by this call.
+ *
+ * Return: The number of folios which were found.
+ * We also update @start to index the next folio for the traversal.
+ */
+unsigned filemap_get_folios(struct address_space *mapping, pgoff_t *start,
+               pgoff_t end, struct folio_batch *fbatch)
+{
+       XA_STATE(xas, &mapping->i_pages, *start);
+       struct folio *folio;
+
+       rcu_read_lock();
+       while ((folio = find_get_entry(&xas, end, XA_PRESENT)) != NULL) {
+               /* Skip over shadow, swap and DAX entries */
+               if (xa_is_value(folio))
+                       continue;
+               if (!folio_batch_add(fbatch, folio)) {
+                       unsigned long nr = folio_nr_pages(folio);
+
+                       if (folio_test_hugetlb(folio))
+                               nr = 1;
+                       *start = folio->index + nr;
+                       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 a 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();
+
+       return folio_batch_count(fbatch);
+}
+EXPORT_SYMBOL(filemap_get_folios);
+
 static inline
 bool folio_more_pages(struct folio *folio, pgoff_t index, pgoff_t max)
 {