[PATCH] fix blk_direct_IO bio preparation

For large size DIO that needs multiple bio, one full page worth of data was
lost at the boundary of bio's maximum sector or segment limits.  After a
bio is full and got submitted.  The outer while (nbytes) { ...  } loop will
allocate a new bio and just march on to index into next page.  It just
forgets about the page that bio_add_page() rejected when previous bio is
full.  Fix it by put the rejected page back to pvec so we pick it up again
for the next bio.

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/block_dev.c b/fs/block_dev.c
index da020be..d9bdf2b 100644 (file)
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -190,6 +190,12 @@ static struct page *blk_get_page(unsigned long addr, size_t count, int rw,
        return pvec->page[pvec->idx++];
 }
 
+/* return a page back to pvec array */
+static void blk_unget_page(struct page *page, struct pvec *pvec)
+{
+       pvec->page[--pvec->idx] = page;
+}
+
 static ssize_t
 blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
                 loff_t pos, unsigned long nr_segs)
@@ -278,6 +284,8 @@ same_bio:
                                count = min(count, nbytes);
                                goto same_bio;
                        }
+               } else {
+                       blk_unget_page(page, &pvec);
                }
 
                /* bio is ready, submit it */