Re: [PATCH mdadm v7 0/7] Write Zeroes option for Creating Arrays

[Chaitanya Kulkarni <chaitanyak@nvidia.com>]

On 3/1/2023 4:38 PM, Jonmichael Hands wrote:
> Hi Logan, Martin,
> just to be clear, the Linux implementation of write zeros is correctly 
> tagging DEAC to 1 during the NVMe write zeros command? This should be 
> very fast on drives that support write zeros with TRIM (most controllers 
> will have the same internal path as a TRIM updating the FTL to 
> deallocate the LBAs). Size of the command really shouldn't affect it 
> much, it is much more correlated with the firmware implementation of above.
> Thanks!
> JM
> Screenshot 2023-03-01 at 4.35.43 PM.png


Yes, it does please see [1].

-ck

1. NVMe DEC bit tagging in NVMe write-zeroes command setup.

static inline blk_status_t nvme_setup_write_zeroes(struct nvme_ns *ns,
		struct request *req, struct nvme_command *cmnd)
{
	memset(cmnd, 0, sizeof(*cmnd));

	if (ns->ctrl->quirks & NVME_QUIRK_DEALLOCATE_ZEROES)
		return nvme_setup_discard(ns, req, cmnd);

	cmnd->write_zeroes.opcode = nvme_cmd_write_zeroes;
	cmnd->write_zeroes.nsid = cpu_to_le32(ns->head->ns_id);
	cmnd->write_zeroes.slba =
		cpu_to_le64(nvme_sect_to_lba(ns, blk_rq_pos(req)));
	cmnd->write_zeroes.length =
		cpu_to_le16((blk_rq_bytes(req) >> ns->lba_shift) - 1);

	if (!(req->cmd_flags & REQ_NOUNMAP) && (ns->features & NVME_NS_DEAC))
		*cmnd->write_zeroes.control |= cpu_to_le16(NVME_WZ_DEAC);*

	if (nvme_ns_has_pi(ns)) {
		cmnd->write_zeroes.control |= cpu_to_le16(NVME_RW_PRINFO_PRACT);

		switch (ns->pi_type) {
		case NVME_NS_DPS_PI_TYPE1:
		case NVME_NS_DPS_PI_TYPE2:
			nvme_set_ref_tag(ns, cmnd, req);
			break;
		}
	}

	return BLK_STS_OK;
}