mm, THP, swap: don't allocate huge cluster for file backed swap device

It's hard to write a whole transparent huge page (THP) to a file backed
swap device during swapping out and the file backed swap device isn't
very popular.  So the huge cluster allocation for the file backed swap
device is disabled.

Link: http://lkml.kernel.org/r/20170724051840.2309-5-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Ross Zwisler <ross.zwisler@intel.com> [for brd.c, zram_drv.c, pmem.c]
Cc: Vishal L Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2bfbfb87123a1f57fcd8448156389c19bdb59c36..267b1fe41844b129c0f0c3e79814c96c4f28a382 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -948,9 +948,10 @@ start_over:
                        spin_unlock(&si->lock);
                        goto nextsi;
                }
-               if (cluster)
-                       n_ret = swap_alloc_cluster(si, swp_entries);
-               else
+               if (cluster) {
+                       if (!(si->flags & SWP_FILE))
+                               n_ret = swap_alloc_cluster(si, swp_entries);
+               } else
                        n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,
                                                    n_goal, swp_entries);
                spin_unlock(&si->lock);