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Re: [dm-devel] Re: dm: bounce_pfn limit added

On Tue, Oct 30, 2007 at 01:11:38PM -0700, Andrew Morton wrote:
> On Mon, 29 Oct 2007 09:31:39 +0300
> Vasily Averin <vvs sw ru> wrote:
> > Device mapper uses its own bounce_pfn that may differ from one on underlying
> > device. In that way dm can build incorrect requests that contain sg elements
> > greater than underlying device is able to handle.
> > This is the cause of slab corruption in i2o layer, occurred on i386 arch when
> > very long direct IO requests are addressed to dm-over-i2o device.

Interesting.  When this patch was originally proposed a couple of years ago, we
did this instead:

) DM doesn't need to bounce bio's on its own, but the block layer defaults
) to that in blk_queue_make_request(). The lower level drivers should
) bounce ios themselves, that is what they need to do if not layered below
) dm anyways.

agk redhat com

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