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From: Fam Zheng <famz@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kwolf@redhat.com, Peter Lieven <pl@kamp.de>,
	qemu-devel@nongnu.org, stefanha@redhat.com
Subject: Re: [Qemu-devel] [RFC PATCH] block: optimize zero writes with bdrv_write_zeroes
Date: Mon, 24 Feb 2014 20:04:13 +0800	[thread overview]
Message-ID: <20140224120413.GB24100@T430.redhat.com> (raw)
In-Reply-To: <530B323C.5050609@redhat.com>

On Mon, 02/24 12:51, Paolo Bonzini wrote:
> Il 24/02/2014 12:33, Fam Zheng ha scritto:
> >> This is (or should be) bdrv_co_write_zeroes without BDRV_REQ_MAY_UNMAP.
> >
> >But IIUC bdrv_co_write_zeroes without BDRV_REQ_MAY_UNMAP doesn't require
> >cluster allocation if it's allocated yet, which is a bit different.
> 
> Yeah, that's why I wrote "or should be".  Those are the intended semantics
> of bdrv_co_write_zeroes without BDRV_REQ_MAY_UNMAP: always allocate a
> cluster that will read as zeroes (allocating even if it does not necessarily
> write the zeroes).
> 
> For legacy reasons it may not be exactly what is implemented.  I asked Kevin
> a couple of weeks ago and he sent a patch, but even he wasn't sure of what
> qcow2 was doing util he looked at the code. :)
> 

I see. I could only tell in VMDK cluster doesn't have this "mapped and zeroed"
state, so maybe we need some flexibility here and reduce assumption.

Fam

  reply	other threads:[~2014-02-24 12:04 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-02-22 13:00 [Qemu-devel] [RFC PATCH] block: optimize zero writes with bdrv_write_zeroes Peter Lieven
2014-02-22 16:45 ` Fam Zheng
2014-02-23 19:10   ` Peter Lieven
2014-02-24  1:01     ` Fam Zheng
2014-02-24 10:39       ` Paolo Bonzini
2014-02-24 11:33         ` Fam Zheng
2014-02-24 11:51           ` Paolo Bonzini
2014-02-24 12:04             ` Fam Zheng [this message]
2014-02-24 12:07             ` Kevin Wolf
2014-02-24 12:10               ` Paolo Bonzini
2014-02-24 12:22                 ` Kevin Wolf
2014-02-24 10:11 ` Kevin Wolf
2014-02-24 10:26   ` Peter Lieven
2014-02-24 10:38     ` Paolo Bonzini
2014-02-24 11:50       ` Peter Lieven
2014-02-24 13:01       ` Peter Lieven
2014-02-25 13:41         ` Kevin Wolf
2014-02-25 17:03           ` Peter Lieven

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