linux-kernel - Re: [PATCH] virtio-blk: add DISCARD support to virtio-blk driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 27 Mar 2017 16:56:26 +0200
From:   Christoph Hellwig <hch@....de>
To:     Changpeng Liu <changpeng.liu@...el.com>
Cc:     virtio-dev@...ts.oasis-open.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, hch@....de, qemu-devel@...gnu.org
Subject: Re: [PATCH] virtio-blk: add DISCARD support to virtio-blk driver

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.