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, 16 insertions, 5 deletions

diff --git a/mm/page_io.c b/mm/page_io.c
index 5f61b54ee1f3..20139b90125a 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -28,16 +28,18 @@
 static struct bio *get_swap_bio(gfp_t gfp_flags,
 				struct page *page, bio_end_io_t end_io)
 {
+	int i, nr = hpage_nr_pages(page);
 	struct bio *bio;
 
-	bio = bio_alloc(gfp_flags, 1);
+	bio = bio_alloc(gfp_flags, nr);
 	if (bio) {
 		bio->bi_iter.bi_sector = map_swap_page(page, &bio->bi_bdev);
 		bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
 		bio->bi_end_io = end_io;
 
-		bio_add_page(bio, page, PAGE_SIZE, 0);
-		BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE);
+		for (i = 0; i < nr; i++)
+			bio_add_page(bio, page + i, PAGE_SIZE, 0);
+		VM_BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE * nr);
 	}
 	return bio;
 }
@@ -262,6 +264,15 @@ static sector_t swap_page_sector(struct page *page)
 	return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
 }
 
+static inline void count_swpout_vm_event(struct page *page)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	if (unlikely(PageTransHuge(page)))
+		count_vm_event(THP_SWPOUT);
+#endif
+	count_vm_events(PSWPOUT, hpage_nr_pages(page));
+}
+
 int __swap_writepage(struct page *page, struct writeback_control *wbc,
 		bio_end_io_t end_write_func)
 {
@@ -313,7 +324,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 
 	ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
 	if (!ret) {
-		count_vm_event(PSWPOUT);
+		count_swpout_vm_event(page);
 		return 0;
 	}
 
@@ -326,7 +337,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 		goto out;
 	}
 	bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc);
-	count_vm_event(PSWPOUT);
+	count_swpout_vm_event(page);
 	set_page_writeback(page);
 	unlock_page(page);
 	submit_bio(bio);