Re: [PATCH] block: respect virtual boundary mask in bvecs

[Ming Lei]

On Tue, Nov 6, 2018 at 8:35 PM Johannes Thumshirn <jthumshirn@xxxxxxx> wrote:
>
> On 05/11/2018 13:01, Ming Lei wrote:
> > If you mean the real huge page, this patch shouldn't have made a difference
> > because bio_vec->bv_offset is in [0, PAGE_SIZE), and iSer sets virt
> > boundary as 4K - 1.
> >
> > However, things will change after multipage bvec is introduced.
>
>
> Hi Ming,
>
> I've received a blktrace from our customer showing the issue [1].
>
> In this example trace they've submitted (contiguous) 64K I/Os and
> without this patch, they're seeing a lot of splits as indicated by the
> trace.
>
> With the patch applied the I/O is directly issued to the LLDD without
> the splits.
>
> [1] http://beta.suse.com/private/jthumshirn/blktrace.txt

blktrace won't help on this issue because .bv_offset isn't recorded.

This patch makes sense on >4KB PAGE_SIZE. If your issue happens on
ARCH with 4K PAGE_SIZE, maybe you should root cause why it makes a
difference on iSer. And it is highly possible there is bug somewhere.

As I mentioned, the description of huge page part in the commit log is
misleading,
and it has to be fixed. Otherwise, the patch itself is fine:

Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>

Thanks
Ming Lei