mm: test code to write THP to swap device as a whole

To support delay splitting THP (Transparent Huge Page) after swapped
out, we need to enhance swap writing code to support to write a THP as a
whole.  This will improve swap write IO performance.

As Ming Lei <ming.lei@redhat.com> pointed out, this should be based on
multipage bvec support, which hasn't been merged yet.  So this patch is
only for testing the functionality of the other patches in the series.
And will be reimplemented after multipage bvec support is merged.

Link: http://lkml.kernel.org/r/20170724051840.2309-7-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.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: Hugh Dickins <hughd@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ross Zwisler <ross.zwisler@intel.com> [for brd.c, zram_drv.c, pmem.c]
Cc: Shaohua Li <shli@kernel.org>
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>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7b1cf4ba0902..1f0720de8990 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -38,7 +38,15 @@
 #define BIO_BUG_ON
 #endif
 
+#ifdef CONFIG_THP_SWAP
+#if HPAGE_PMD_NR > 256
+#define BIO_MAX_PAGES           HPAGE_PMD_NR
+#else
 #define BIO_MAX_PAGES           256
+#endif
+#else
+#define BIO_MAX_PAGES           256
+#endif
 
 #define bio_prio(bio)                   (bio)->bi_ioprio
 #define bio_set_prio(bio, prio)         ((bio)->bi_ioprio = prio)