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SubjectRE: [patch] optimize o_direct on block device - v3
Randy Dunlap wrote on Thursday, January 11, 2007 1:45 PM
> > +/* return a pge back to pvec array */
> is pge just a typo or some other tla that i don't know?
> (not portland general electric or pacific gas & electric)

Typo with fat fingers. Thanks for catching it. Full patch with typo fixed.

[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 forget 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 <>

diff -Nurp linux-2.6.20-rc4/fs/block_dev.c linux-2.6.20.ken/fs/block_dev.c
--- linux-2.6.20-rc4/fs/block_dev.c 2007-01-06 21:45:51.000000000 -0800
+++ linux-2.6.20.ken/fs/block_dev.c 2007-01-10 19:54:53.000000000 -0800
@@ -190,6 +190,12 @@ static struct page *blk_get_page(unsigne
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 */
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