From: "Richard W.M. Jones" <rjones@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Teng-Feng Yang <shinrairis@gmail.com>, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] TRIM/DISCARD/UNMAP support on qemu-nbd
Date: Wed, 8 Jan 2014 22:53:54 +0000 [thread overview]
Message-ID: <20140108225354.GQ4802@redhat.com> (raw)
In-Reply-To: <52CDD513.80408@redhat.com>
On Wed, Jan 08, 2014 at 11:45:39PM +0100, Paolo Bonzini wrote:
> Il 08/01/2014 23:24, Richard W.M. Jones ha scritto:
> > It's extremely difficult to know when it's safe to add this parameter.
> > Qemu gives no indication of when using discard=.. is safe (ie. won't
> > cause qemu to fail to start up or fail in some other way). It's even
> > worse when we have to go via libvirt which itself doesn't expose
> > qemu's capabilities upwards.
>
> It is a bug that "-help" doesn't list discard=on, but QMP
> query-command-line-options lists it correctly.
>
> libvirt could safely ignore discard if the underlying QEMU does not
> support it, but that's not how it was implemented. Currently,
> explicitly specifying either discard='on' and discard='off' will cause
> the VM to fail to start if QEMU does not support it. There are
> tradeoffs in both solutions...
That sucks .. for me ...
Can't we have an option like discard=ifpossible? libguestfs would use
this, since we'd always prefer to honour discard requests from our
kernel.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-p2v converts physical machines to virtual machines. Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v
next prev parent reply other threads:[~2014-01-08 22:54 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-30 11:58 [Qemu-devel] TRIM/DISCARD/UNMAP support on qemu-nbd Teng-Feng Yang
2014-01-02 16:15 ` Richard W.M. Jones
2014-01-07 14:48 ` Paolo Bonzini
2014-01-07 20:27 ` Richard W.M. Jones
2014-01-07 20:48 ` Paolo Bonzini
2014-01-07 21:22 ` Richard W.M. Jones
2014-01-08 22:11 ` Paolo Bonzini
2014-01-08 22:24 ` Richard W.M. Jones
2014-01-08 22:45 ` Paolo Bonzini
2014-01-08 22:53 ` Richard W.M. Jones [this message]
2014-01-09 7:02 ` Paolo Bonzini
2014-01-07 21:27 ` Richard W.M. Jones
2014-01-06 2:45 ` Stefan Hajnoczi
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