[PATCH] mm: swap write failure fixup

Currently we can silently drop data if the write to swap failed.  It
usually doesn't result in data-corruption because on page-in the process
will receive SIGBUS (assuming write-failure implies read-failure).

This assumption might or might not be valid.

This patch will avoid the page being discarded after a failed write.  But
will print a warning the sysadmin _should_ take to heart, if a lot of swap
space becomes un-writeable, OOM is not far off.

Tested by making the write fail 'randomly' once every 50 writes or so.

[akpm@osdl.org: printk warning fix]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/mm/page_io.c b/mm/page_io.c
index 8802994..d2f0a57 100644 (file)
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -52,8 +52,23 @@ static int end_swap_bio_write(struct bio *bio, unsigned int bytes_done, int err)
        if (bio->bi_size)
                return 1;
 
-       if (!uptodate)
+       if (!uptodate) {
                SetPageError(page);
+               /*
+                * We failed to write the page out to swap-space.
+                * Re-dirty the page in order to avoid it being reclaimed.
+                * Also print a dire warning that things will go BAD (tm)
+                * very quickly.
+                *
+                * Also clear PG_reclaim to avoid rotate_reclaimable_page()
+                */
+               set_page_dirty(page);
+               printk(KERN_ALERT "Write-error on swap-device (%u:%u:%Lu)\n",
+                               imajor(bio->bi_bdev->bd_inode),
+                               iminor(bio->bi_bdev->bd_inode),
+                               (unsigned long long)bio->bi_sector);
+               ClearPageReclaim(page);
+       }
        end_page_writeback(page);
        bio_put(bio);
        return 0;
@@ -70,6 +85,10 @@ static int end_swap_bio_read(struct bio *bio, unsigned int bytes_done, int err)
        if (!uptodate) {
                SetPageError(page);
                ClearPageUptodate(page);
+               printk(KERN_ALERT "Read-error on swap-device (%u:%u:%Lu)\n",
+                               imajor(bio->bi_bdev->bd_inode),
+                               iminor(bio->bi_bdev->bd_inode),
+                               (unsigned long long)bio->bi_sector);
        } else {
                SetPageUptodate(page);
        }