mm: clarify the radix_tree exceptional cases

Make the radix_tree exceptional cases, mostly in filemap.c, clearer.

It's hard to devise a suitable snappy name that illuminates the use by
shmem/tmpfs for swap, while keeping filemap/pagecache/radix_tree
generality.  And akpm points out that /* radix_tree_deref_retry(page) */
comments look like calls that have been commented out for unknown
reason.

Skirt the naming difficulty by rearranging these blocks to handle the
transient radix_tree_deref_retry(page) case first; then just explain the
remaining shmem/tmpfs swap case in a comment.

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 1c702f6f1241..32f6763f16fb 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -332,10 +332,14 @@ repeat:
                 if (unlikely(!page))
                         continue;
                 if (radix_tree_exception(page)) {
-                        if (radix_tree_exceptional_entry(page))
-                                goto export;
-                        /* radix_tree_deref_retry(page) */
-                        goto restart;
+                        if (radix_tree_deref_retry(page))
+                                goto restart;
+                        /*
+                         * Otherwise, we must be storing a swap entry
+                         * here as an exceptional entry: so return it
+                         * without attempting to raise page count.
+                         */
+                        goto export;
                 }
                 if (!page_cache_get_speculative(page))
                         goto repeat;