Re: [Qemu-devel] [PATCH 4/4] block: Cater to iscsi with non-power-of-2 discard

[Peter Lieven]

Am 25.10.2016 um 14:09 schrieb Paolo Bonzini:
> On 25/10/2016 14:03, Peter Lieven wrote:
> > Am 01.08.2016 um 11:22 schrieb Paolo Bonzini:
> > > On 28/07/2016 04:39, Eric Blake wrote:
> > > > On 07/27/2016 01:25 AM, Fam Zheng wrote:
> > > > > On Thu, 07/21 13:34, Eric Blake wrote:
> > > > > > +    max_write_zeroes = max_write_zeroes / alignment * alignment;
> > > > > Not using QEMU_ALIGN_DOWN despite patch 3?
> > > > Looks like I missed that on the rebase. Can fix if there is a reason for
> > > > a respin.
> > > Since Stefan acked this, I'm applying the patch and fixing it to use
> > > QEMU_ALIGN_DOWN.
> > >
> > > Paolo
> > Hi,
> >
> > I came across a sort of regression we introduced with the dropping of
> > head and tail
> > of an unaligned discard.
> >
> > The discard alignment that we use to trim the discard request is just a
> > hint.
> >
> > I learned on the equallogics that a page (which is this unusal 15MB
> > large) is
> > unallocated even if the discard happens in pieces. E.g. in slices of 1MB
> > requests.
> >
> >  From my point of view I would like to restore the old behaviour. What do
> > you think?
> The right logic should be the one in Linux: if splitting a request, and
> the next starting sector would be misaligned, stop the discard at the
> previous aligned sector.  Otherwise leave everything alone.

Just to clarify. I mean the guest would send incremental 1MB discards
we would now drop all of them if the alignment is 15MB. Previously,
we have sent all of the 1MB requests.

Peter