From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org
Cc: berto@igalia.com, qemu-devel@nongnu.org, mreitz@redhat.com
Subject: Re: [PATCH v7 10/10] qcow2: Forward ZERO_WRITE flag for full preallocation
Date: Fri, 24 Apr 2020 18:26:03 +0300 [thread overview]
Message-ID: <4ea6fa46-3668-4553-5956-ac314631dd63@virtuozzo.com> (raw)
In-Reply-To: <20200424142701.67053-1-kwolf@redhat.com>
24.04.2020 17:27, Kevin Wolf wrote:
> The BDRV_REQ_ZERO_WRITE is currently implemented in a way that first the
> image is possibly preallocated and then the zero flag is added to all
> clusters. This means that a copy-on-write operation may be needed when
> writing to these clusters, despite having used preallocation, negating
> one of the major benefits of preallocation.
>
> Instead, try to forward the BDRV_REQ_ZERO_WRITE to the protocol driver,
> and if the protocol driver can ensure that the new area reads as zeros,
> we can skip setting the zero flag in the qcow2 layer.
>
> Unfortunately, the same approach doesn't work for metadata
> preallocation, so we'll still set the zero flag there.
>
> Signed-off-by: Kevin Wolf<kwolf@redhat.com>
> Reviewed-by: Max Reitz<mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
--
Best regards,
Vladimir
next prev parent reply other threads:[~2020-04-24 15:27 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-24 12:54 [PATCH v7 00/10] block: Fix resize (extending) of short overlays Kevin Wolf
2020-04-24 12:54 ` [PATCH v7 01/10] block: Add flags to BlockDriver.bdrv_co_truncate() Kevin Wolf
2020-04-24 12:54 ` [PATCH v7 02/10] block: Add flags to bdrv(_co)_truncate() Kevin Wolf
2020-04-24 12:54 ` [PATCH v7 03/10] block-backend: Add flags to blk_truncate() Kevin Wolf
2020-04-24 12:54 ` [PATCH v7 04/10] qcow2: Support BDRV_REQ_ZERO_WRITE for truncate Kevin Wolf
2020-04-24 14:07 ` Max Reitz
2020-04-24 14:39 ` Eric Blake
2020-04-28 16:28 ` Eric Blake
2020-04-28 18:45 ` Kevin Wolf
2020-04-28 18:58 ` Eric Blake
2020-04-24 12:54 ` [PATCH v7 05/10] raw-format: " Kevin Wolf
2020-04-24 12:54 ` [PATCH v7 06/10] file-posix: " Kevin Wolf
2020-04-24 12:54 ` [PATCH v7 07/10] block: truncate: Don't make backing file data visible Kevin Wolf
2020-04-24 14:09 ` Max Reitz
2020-04-24 12:54 ` [PATCH v7 08/10] iotests: Filter testfiles out in filter_img_info() Kevin Wolf
2020-04-24 12:54 ` [PATCH v7 09/10] iotests: Test committing to short backing file Kevin Wolf
2020-04-24 14:14 ` Max Reitz
2020-04-24 14:49 ` Vladimir Sementsov-Ogievskiy
2020-04-24 14:16 ` [PATCH v7 00/10] block: Fix resize (extending) of short overlays Max Reitz
2020-04-24 14:27 ` [PATCH v7 10/10] qcow2: Forward ZERO_WRITE flag for full preallocation Kevin Wolf
2020-04-24 14:28 ` Max Reitz
2020-04-24 15:26 ` Vladimir Sementsov-Ogievskiy [this message]
2020-04-27 15:43 ` [PATCH v7 00/10] block: Fix resize (extending) of short overlays Kevin Wolf
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