mm/filemap.c: add comment for confusing logic in page_cache_tree_insert()

Unlike THP, hugetlb pages are represented by one entry in the
radix-tree.

[akpm@linux-foundation.org: tweak comment]
Link: http://lkml.kernel.org/r/20161110163640.126124-1-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 50b52fe51937..caa779f8797f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -169,7 +169,10 @@ static int page_cache_tree_insert(struct address_space *mapping,
 static void page_cache_tree_delete(struct address_space *mapping,
                                    struct page *page, void *shadow)
 {
-        int i, nr = PageHuge(page) ? 1 : hpage_nr_pages(page);
+        int i, nr;
+
+        /* hugetlb pages are represented by one entry in the radix tree */
+        nr = PageHuge(page) ? 1 : hpage_nr_pages(page);
 
         VM_BUG_ON_PAGE(!PageLocked(page), page);
         VM_BUG_ON_PAGE(PageTail(page), page);