From: Stefan Hajnoczi <stefanha@gmail.com>
To: Jun Li <junmuzi@gmail.com>
Cc: kwolf@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com
Subject: Re: [Qemu-devel] [PATCH v2] qcow2: Add bdrv_discard support
Date: Wed, 27 Aug 2014 15:12:42 +0100 [thread overview]
Message-ID: <20140827141242.GQ8280@stefanha-thinkpad.redhat.com> (raw)
In-Reply-To: <53FA14EE.2060104@gmail.com>
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On Mon, Aug 25, 2014 at 12:38:06AM +0800, Jun Li wrote:
> Why bdrv_discard does not yet pass the discard on to the underlying file
> system driver? And this exist a potential issue: host cluster leak for
> qcow2. As qcow2 image can be created on RAW disk,
> so this is not just "does not yet pass the discard on to the underlying file
> system driver". Could you give some explanation why do not realize this
> function? Thx.
>
> As I am trying to realize qcow2 shrinking, but hit bdrv_discard can not
> release the free cluster on host.
qcow2 is capable of passing discards down to the image file. See
qcow2_process_discards().
It is important that s->discard_passthrough[QCOW2_DISCARD_REQUEST] is
true! Make sure to use the pass-discard-request=on or discard=unmap
options.
Stefan
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next prev parent reply other threads:[~2014-08-27 14:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-24 16:38 [Qemu-devel] [PATCH v2] qcow2: Add bdrv_discard support Jun Li
2014-08-27 14:12 ` Stefan Hajnoczi [this message]
-- strict thread matches above, loose matches on Subject: below --
2011-01-28 11:41 Kevin Wolf
2011-01-28 12:46 ` Stefan Hajnoczi
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