> -----Original Message----- > From: Christoph Hellwig [mailto:hch@xxxxxx] > Sent: Monday, March 27, 2017 10:56 PM > To: Liu, Changpeng <changpeng.liu@xxxxxxxxx> > Cc: virtio-dev@xxxxxxxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx; hch@xxxxxx; qemu-devel@xxxxxxxxxx > 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. Not yet, patch goes first, there are uses who don't want to migrate from virtio-blk to virtio-scsi, so this feature seems reasonable, the question is that how we should define the specification to support this 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. For support multi-range discard features, the DISCARD command must have data_in buffer, similar with SCSI UNMAP and NVMe DEALLOCATE commands, maybe 16 bytes aligned descriptors are required for each DISCARD command. > > > + 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. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
