swap: use bdev_read_page() / bdev_write_page()

By calling the device driver to write the page directly, we avoid
allocating a BIO, which allows us to free memory without allocating
memory.

[akpm@linux-foundation.org: fix used-uninitialized bug]
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dheeraj Reddy <dheeraj.reddy@intel.com>
Cc: 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, 20 insertions, 1 deletions

diff --git a/mm/page_io.c b/mm/page_io.c
index 7c59ef681381..58b50d2901fe 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -248,11 +248,16 @@ out:
         return ret;
 }
 
+static sector_t swap_page_sector(struct page *page)
+{
+        return (sector_t)__page_file_index(page) << (PAGE_CACHE_SHIFT - 9);
+}
+
 int __swap_writepage(struct page *page, struct writeback_control *wbc,
         void (*end_write_func)(struct bio *, int))
 {
         struct bio *bio;
-        int ret = 0, rw = WRITE;
+        int ret, rw = WRITE;
         struct swap_info_struct *sis = page_swap_info(page);
 
         if (sis->flags & SWP_FILE) {
@@ -297,6 +302,13 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
                 return ret;
         }
 
+        ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
+        if (!ret) {
+                count_vm_event(PSWPOUT);
+                return 0;
+        }
+
+        ret = 0;
         bio = get_swap_bio(GFP_NOIO, page, end_write_func);
         if (bio == NULL) {
                 set_page_dirty(page);
@@ -338,6 +350,13 @@ int swap_readpage(struct page *page)
                 return ret;
         }
 
+        ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
+        if (!ret) {
+                count_vm_event(PSWPIN);
+                return 0;
+        }
+
+        ret = 0;
         bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
         if (bio == NULL) {
                 unlock_page(page);