mm: add find_get_entries_tag()

Add find_get_entries_tag() to the family of functions that include
find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
needed for DAX dirty page handling because we need a list of both page
offsets and radix tree entries ('indices' and 'entries' in this
function) that are marked with the PAGECACHE_TAG_TOWRITE tag.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jeff Layton <jlayton@poochiereds.net>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Matthew Wilcox <matthew.r.wilcox@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 68 insertions, 0 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 7b8be78cfd9e..1e215fc36c83 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1499,6 +1499,74 @@ repeat:
 }
 EXPORT_SYMBOL(find_get_pages_tag);
 
+/**
+ * find_get_entries_tag - find and return entries that match @tag
+ * @mapping:    the address_space to search
+ * @start:      the starting page cache index
+ * @tag:        the tag index
+ * @nr_entries: the maximum number of entries
+ * @entries:    where the resulting entries are placed
+ * @indices:    the cache indices corresponding to the entries in @entries
+ *
+ * Like find_get_entries, except we only return entries which are tagged with
+ * @tag.
+ */
+unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
+                        int tag, unsigned int nr_entries,
+                        struct page **entries, pgoff_t *indices)
+{
+        void **slot;
+        unsigned int ret = 0;
+        struct radix_tree_iter iter;
+
+        if (!nr_entries)
+                return 0;
+
+        rcu_read_lock();
+restart:
+        radix_tree_for_each_tagged(slot, &mapping->page_tree,
+                                   &iter, start, tag) {
+                struct page *page;
+repeat:
+                page = radix_tree_deref_slot(slot);
+                if (unlikely(!page))
+                        continue;
+                if (radix_tree_exception(page)) {
+                        if (radix_tree_deref_retry(page)) {
+                                /*
+                                 * Transient condition which can only trigger
+                                 * when entry at index 0 moves out of or back
+                                 * to root: none yet gotten, safe to restart.
+                                 */
+                                goto restart;
+                        }
+
+                        /*
+                         * A shadow entry of a recently evicted page, a swap
+                         * entry from shmem/tmpfs or a DAX entry.  Return it
+                         * without attempting to raise page count.
+                         */
+                        goto export;
+                }
+                if (!page_cache_get_speculative(page))
+                        goto repeat;
+
+                /* Has the page moved? */
+                if (unlikely(page != *slot)) {
+                        page_cache_release(page);
+                        goto repeat;
+                }
+export:
+                indices[ret] = iter.index;
+                entries[ret] = page;
+                if (++ret == nr_entries)
+                        break;
+        }
+        rcu_read_unlock();
+        return ret;
+}
+EXPORT_SYMBOL(find_get_entries_tag);
+
 /*
  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
  * a _large_ part of the i/o request. Imagine the worst scenario: