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SubjectRe: [patch] optimize o_direct on block device - v3
On Thu, 11 Jan 2007 13:36:28 -0800 Chen, Kenneth W wrote:

> Andrew Morton wrote on Thursday, January 11, 2007 11:29 AM
> > On Thu, 11 Jan 2007 13:21:57 -0600
> > Michael Reed <mdr@sgi.com> wrote:
> > > Testing on my ia64 system reveals that this patch introduces a
> > > data integrity error for direct i/o to a block device. Device
> > > errors which result in i/o failure do not propagate to the
> > > process issuing direct i/o to the device.
> > >
> > > This can be reproduced by doing writes to a fibre channel block
> > > device and then disabling the switch port connecting the host
> > > adapter to the switch.
> > >
> >
> > Does this fix it?
> >
> > <thwaps Ken>
>
>
> Darn, kicking myself in the butt. Thank you Andrew for fixing this.
> We've also running DIO stress test almost non-stop over the last 30
> days or so and we did uncover another bug in that patch.
>
> Andrew, would you please take the follow bug fix patch as well. It
> is critical because it also affects data integrity.
>
>
> [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 <kenneth.w.chen@intel.com>
>
> 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 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)

> +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 */
> -


---
~Randy
-
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