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From: Rusty Russell <rusty@rustcorp.com.au>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Frank Swiderski <fes@google.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Rik van Riel <riel@redhat.com>, Rafael Aquini <aquini@redhat.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	mikew@google.com, Ying Han <yinghan@google.com>,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH] Add a page cache-backed balloon device driver.
Date: Thu, 06 Sep 2012 11:05:12 +0930	[thread overview]
Message-ID: <87sjawhr1r.fsf@rustcorp.com.au> (raw)
In-Reply-To: <50444FAF.7030304@redhat.com>

Paolo Bonzini <pbonzini@redhat.com> writes:
> Il 02/07/2012 02:29, Rusty Russell ha scritto:
>> VIRTIO_BALLOON_F_MUST_TELL_HOST
>> implies you should tell the host (eventually).  I don't know if any
>> implementations actually care though.
>
> This is indeed broken, because it is a "negative" feature: it tells you
> that "implicit deflate" is _not_ supported.
>
> Right now, QEMU refuses migration if the target does not support all the
> features that were negotiated.  But then:
>
> - a migration from non-MUST_TELL_HOST to MUST_TELL_HOST will succeed,
> which is wrong;
>
> - a migration from MUST_TELL_HOST to non-MUST_TELL_HOST will fail, which
> is useless.
>
>> We could add a VIRTIO_BALLOON_F_NEVER_TELL_DEFLATE which would mean the
>> deflate vq need not be used at all.
>
> That would work.  At the same time we could deprecate MUST_TELL_HOST.
> Certainly the guest implementations don't care, or we would have
> experienced problems such as the one above.  The QEMU implementation
> also does not care but, for example, a Xen implementation would care.

OK; I'm not sure we need to deprecate MUST_TELL_HOST, though since it's
never actually been used there's a good argument.

VIRTIO_BALLOON_F_SILENT_DEFLATE (or whatever it's called) would
obviously mean you couldn't ack VIRTIO_BALLOON_F_MUST_TELL_HOST.

Patches welcome!

Cheers,
Rusty.

WARNING: multiple messages have this Message-ID (diff)
From: Rusty Russell <rusty@rustcorp.com.au>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Frank Swiderski <fes@google.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Rik van Riel <riel@redhat.com>, Rafael Aquini <aquini@redhat.com>,
	kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
	linux-kernel@vger.kernel.org, mikew@google.com,
	Ying Han <yinghan@google.com>,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH] Add a page cache-backed balloon device driver.
Date: Thu, 06 Sep 2012 11:05:12 +0930	[thread overview]
Message-ID: <87sjawhr1r.fsf@rustcorp.com.au> (raw)
In-Reply-To: <50444FAF.7030304@redhat.com>

Paolo Bonzini <pbonzini@redhat.com> writes:
> Il 02/07/2012 02:29, Rusty Russell ha scritto:
>> VIRTIO_BALLOON_F_MUST_TELL_HOST
>> implies you should tell the host (eventually).  I don't know if any
>> implementations actually care though.
>
> This is indeed broken, because it is a "negative" feature: it tells you
> that "implicit deflate" is _not_ supported.
>
> Right now, QEMU refuses migration if the target does not support all the
> features that were negotiated.  But then:
>
> - a migration from non-MUST_TELL_HOST to MUST_TELL_HOST will succeed,
> which is wrong;
>
> - a migration from MUST_TELL_HOST to non-MUST_TELL_HOST will fail, which
> is useless.
>
>> We could add a VIRTIO_BALLOON_F_NEVER_TELL_DEFLATE which would mean the
>> deflate vq need not be used at all.
>
> That would work.  At the same time we could deprecate MUST_TELL_HOST.
> Certainly the guest implementations don't care, or we would have
> experienced problems such as the one above.  The QEMU implementation
> also does not care but, for example, a Xen implementation would care.

OK; I'm not sure we need to deprecate MUST_TELL_HOST, though since it's
never actually been used there's a good argument.

VIRTIO_BALLOON_F_SILENT_DEFLATE (or whatever it's called) would
obviously mean you couldn't ack VIRTIO_BALLOON_F_MUST_TELL_HOST.

Patches welcome!

Cheers,
Rusty.

  reply	other threads:[~2012-09-06  3:03 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-06-26 20:32 [PATCH] Add a page cache-backed balloon device driver Frank Swiderski
2012-06-26 20:40 ` Rik van Riel
2012-06-26 20:40   ` Rik van Riel
2012-06-26 21:31   ` Frank Swiderski
2012-06-26 21:31     ` Frank Swiderski
2012-06-26 21:45     ` Rik van Riel
2012-06-26 21:45       ` Rik van Riel
2012-06-26 23:45       ` Frank Swiderski
2012-06-27  9:04         ` Michael S. Tsirkin
2012-06-27  9:04           ` Michael S. Tsirkin
2012-06-26 21:47     ` Michael S. Tsirkin
2012-06-26 21:47       ` Michael S. Tsirkin
2012-06-26 23:21       ` Frank Swiderski
2012-06-26 23:21         ` Frank Swiderski
2012-06-27  9:02         ` Michael S. Tsirkin
2012-06-27  9:02           ` Michael S. Tsirkin
2012-07-02  0:29         ` Rusty Russell
2012-07-02  0:29           ` Rusty Russell
2012-09-03  6:35           ` Paolo Bonzini
2012-09-03  6:35             ` Paolo Bonzini
2012-09-06  1:35             ` Rusty Russell [this message]
2012-09-06  1:35               ` Rusty Russell
2012-06-26 21:41 ` Michael S. Tsirkin
2012-06-26 21:41   ` Michael S. Tsirkin
2012-06-27  2:56   ` Rusty Russell
2012-06-27  2:56     ` Rusty Russell
2012-06-27 15:48     ` Frank Swiderski
2012-06-27 15:48       ` Frank Swiderski
2012-06-27 16:06       ` Michael S. Tsirkin
2012-06-27 16:06         ` Michael S. Tsirkin
2012-06-27 16:08         ` Frank Swiderski
2012-06-27 16:08           ` Frank Swiderski
2012-06-27  9:40 ` Amit Shah
2012-06-27  9:40   ` Amit Shah
2012-08-30  8:57 ` Michael S. Tsirkin
2012-08-30  8:57   ` Michael S. Tsirkin
2012-09-03 15:09 ` Avi Kivity
2012-09-03 15:09   ` Avi Kivity
2012-09-10  9:05 ` Michael S. Tsirkin
2012-09-10  9:05   ` Michael S. Tsirkin
2012-09-10 17:37   ` Mike Waychison
2012-09-10 17:37     ` Mike Waychison
2012-09-10 18:04     ` Rik van Riel
2012-09-10 18:04       ` Rik van Riel
2012-09-10 18:29       ` Mike Waychison
2012-09-10 18:29         ` Mike Waychison
2012-09-10 19:59     ` Michael S. Tsirkin
2012-09-10 19:59       ` Michael S. Tsirkin
2012-09-10 19:59       ` Michael S. Tsirkin
2012-09-10 20:49       ` Mike Waychison
2012-09-10 20:49         ` Mike Waychison
2012-09-10 21:10         ` Michael S. Tsirkin
2012-09-10 21:10           ` Michael S. Tsirkin
2012-10-30 15:29           ` Michael S. Tsirkin
2012-10-30 15:29             ` Michael S. Tsirkin
2012-10-30 16:25             ` Mike Waychison
2012-10-30 16:25               ` Mike Waychison
2012-09-12  5:25         ` Rusty Russell
2012-09-12  5:25           ` Rusty Russell
2012-06-26 20:32 Frank Swiderski

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