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. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
