mm: account skipped entries to avoid looping in find_get_pages

The found entries by find_get_pages() could be all swap entries.  In
this case we skip the entries, but make sure the skipped entries are
accounted, so we don't keep looping.

Using nr_found > nr_skip to simplify code as suggested by Eric.

Reported-and-tested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 645a080ba4d..7771871fa35 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -827,13 +827,14 @@ unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
 {
         unsigned int i;
         unsigned int ret;
-        unsigned int nr_found;
+        unsigned int nr_found, nr_skip;
 
         rcu_read_lock();
 restart:
         nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
                                 (void ***)pages, NULL, start, nr_pages);
         ret = 0;
+        nr_skip = 0;
         for (i = 0; i < nr_found; i++) {
                 struct page *page;
 repeat:
@@ -856,6 +857,7 @@ repeat:
                          * here as an exceptional entry: so skip over it -
                          * we only reach this from invalidate_mapping_pages().
                          */
+                        nr_skip++;
                         continue;
                 }
 
@@ -876,7 +878,7 @@ repeat:
          * If all entries were removed before we could secure them,
          * try again, because callers stop trying once 0 is returned.
          */
-        if (unlikely(!ret && nr_found))
+        if (unlikely(!ret && nr_found > nr_skip))
                 goto restart;
         rcu_read_unlock();
         return ret;