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-rw-r--r--mm/page_io.c50
1 files changed, 48 insertions, 2 deletions
diff --git a/mm/page_io.c b/mm/page_io.c
index a8a3ef45fed..ba05b64e5d8 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -21,6 +21,7 @@
#include <linux/writeback.h>
#include <linux/frontswap.h>
#include <linux/aio.h>
+#include <linux/blkdev.h>
#include <asm/pgtable.h>
static struct bio *get_swap_bio(gfp_t gfp_flags,
@@ -80,9 +81,54 @@ void end_swap_bio_read(struct bio *bio, int err)
imajor(bio->bi_bdev->bd_inode),
iminor(bio->bi_bdev->bd_inode),
(unsigned long long)bio->bi_sector);
- } else {
- SetPageUptodate(page);
+ goto out;
}
+
+ SetPageUptodate(page);
+
+ /*
+ * There is no guarantee that the page is in swap cache - the software
+ * suspend code (at least) uses end_swap_bio_read() against a non-
+ * swapcache page. So we must check PG_swapcache before proceeding with
+ * this optimization.
+ */
+ if (likely(PageSwapCache(page))) {
+ struct swap_info_struct *sis;
+
+ sis = page_swap_info(page);
+ if (sis->flags & SWP_BLKDEV) {
+ /*
+ * The swap subsystem performs lazy swap slot freeing,
+ * expecting that the page will be swapped out again.
+ * So we can avoid an unnecessary write if the page
+ * isn't redirtied.
+ * This is good for real swap storage because we can
+ * reduce unnecessary I/O and enhance wear-leveling
+ * if an SSD is used as the as swap device.
+ * But if in-memory swap device (eg zram) is used,
+ * this causes a duplicated copy between uncompressed
+ * data in VM-owned memory and compressed data in
+ * zram-owned memory. So let's free zram-owned memory
+ * and make the VM-owned decompressed page *dirty*,
+ * so the page should be swapped out somewhere again if
+ * we again wish to reclaim it.
+ */
+ struct gendisk *disk = sis->bdev->bd_disk;
+ if (disk->fops->swap_slot_free_notify) {
+ swp_entry_t entry;
+ unsigned long offset;
+
+ entry.val = page_private(page);
+ offset = swp_offset(entry);
+
+ SetPageDirty(page);
+ disk->fops->swap_slot_free_notify(sis->bdev,
+ offset);
+ }
+ }
+ }
+
+out:
unlock_page(page);
bio_put(bio);
}