From: Christoph Hellwig <hch@lst.de>
To: Changpeng Liu <changpeng.liu@intel.com>
Cc: virtio-dev@lists.oasis-open.org,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, hch@lst.de, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] virtio-blk: add DISCARD support to virtio-blk driver
Date: Mon, 27 Mar 2017 16:56:26 +0200 [thread overview]
Message-ID: <20170327145625.GA24952@lst.de> (raw)
In-Reply-To: <1490690365-21109-1-git-send-email-changpeng.liu@intel.com>
On Tue, Mar 28, 2017 at 04:39:25PM +0800, Changpeng Liu wrote:
> Currently virtio-blk driver does not provide discard feature flag, so the
> filesystems which built on top of the block device will not send discard
> command. This is okay for HDD backend, but it will impact the performance
> for SSD backend.
>
> Add a feature flag VIRTIO_BLK_F_DISCARD and command VIRTIO_BLK_T_DISCARD
> to extend exist virtio-blk protocol. virtio-blk protocol uses a single
> 8 bytes descriptor containing type,reserved and sector, currently Linux
> uses the reserved field as IO priority, here we also re-use the reserved
> field as number of discard sectors.
Do you have a link to the specification for this feature? At least
virtio-v1.0 does not seem to specify a discard feature.
Note that Linux 4.11 and later have support for multi-range discard
ala ATA TRIM, SCSI UNMAP and NVMe deallocate which might be useful
here, too.
> + q->limits.discard_zeroes_data = 0;
No need to clear this. Also hopefully this field goes away for 4.12
> + blk_queue_max_discard_segments(q, 1);
No need to set this.
next prev parent reply other threads:[~2017-03-27 14:56 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-28 8:39 [Qemu-devel] [PATCH] virtio-blk: add DISCARD support to virtio-blk driver Changpeng Liu
2017-03-27 11:34 ` [Qemu-devel] [virtio-dev] " Paolo Bonzini
2017-03-28 1:52 ` Liu, Changpeng
2017-03-27 14:56 ` Christoph Hellwig [this message]
2017-03-28 1:43 ` [Qemu-devel] " Liu, Changpeng
2017-03-27 20:20 ` Stefan Hajnoczi
2017-03-28 2:15 ` Liu, Changpeng
2017-03-28 8:37 ` Stefan Hajnoczi
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