linux-kernel - Re: virtio_blk: fix defaults for max_hw_sectors and max_segment

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Date:	Wed, 26 Nov 2014 16:51:08 -0500
From:	Mike Snitzer <snitzer@...hat.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Christoph Hellwig <hch@...radead.org>, martin.petersen@...cle.com,
	mst@...hat.com, rusty@...tcorp.com.au,
	linux-kernel@...r.kernel.org, qemu-devel@...gnu.org,
	dm-devel@...hat.com, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: virtio_blk: fix defaults for max_hw_sectors and max_segment_size

On Wed, Nov 26 2014 at  3:54pm -0500,
Jens Axboe <axboe@...nel.dk> wrote:

> On 11/26/2014 01:51 PM, Mike Snitzer wrote:
> > On Wed, Nov 26 2014 at  2:48pm -0500,
> > Jens Axboe <axboe@...nel.dk> wrote:
> > 
> >>
> >> That code isn't even in mainline, as far as I can tell...
> > 
> > Right, it is old RHEL6 code.
> > 
> > But I've yet to determine what changed upstream that enables this to
> > "just work" with a really large max_sectors (I haven't been looking
> > either).
> 
> Kind of hard for the rest of us to say, since it's triggering a BUG in
> code we don't have :-)

I never asked you or others to weigh in on old RHEL6 code.  Once I
realized upstream worked even if max_sectors is _really_ high I said
"sorry for the noise".

But while you're here, I wouldn't mind getting your take on virtio-blk
setting max_hw_sectors to -1U.

As I said in my original reply to mst: it only makes sense to set a
really high initial upper bound like that in a driver if that driver
goes on to stack an underlying device's limit.
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