From: Paolo Bonzini <pbonzini@redhat.com>
To: Fam Zheng <famz@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 12:51:24 +0100 [thread overview]
Message-ID: <530B323C.5050609@redhat.com> (raw)
In-Reply-To: <20140224113311.GA24100@T430.redhat.com>
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. :)
Paolo
next prev parent reply other threads:[~2014-02-24 11:51 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 [this message]
2014-02-24 12:04 ` Fam Zheng
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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