Re: [PATCH v2 2/4] On Discard either do Reset WP or Write Same
Shaun,
On 8/22/16 13:31, Shaun Tancheff wrote:
[...]
> -int sd_zbc_setup_discard(struct scsi_disk *sdkp, struct request *rq,
> - sector_t sector, unsigned int num_sectors)
> +int sd_zbc_setup_discard(struct scsi_cmnd *cmd)
> {
> - struct blk_zone *zone;
> + struct request *rq = cmd->request;
> + struct scsi_device *sdp = cmd->device;
> + struct scsi_disk *sdkp = scsi_disk(rq->rq_disk);
> + sector_t sector = blk_rq_pos(rq);
> + unsigned int nr_sectors = blk_rq_sectors(rq);
> int ret = BLKPREP_OK;
> + struct blk_zone *zone;
> unsigned long flags;
> + u32 wp_offset;
> + bool use_write_same = false;
>
> zone = blk_lookup_zone(rq->q, sector);
> - if (!zone)
> + if (!zone) {
> + /* Test for a runt zone before giving up */
> + if (sdp->type != TYPE_ZBC) {
> + struct request_queue *q = rq->q;
> + struct rb_node *node;
> +
> + node = rb_last(&q->zones);
> + if (node)
> + zone = rb_entry(node, struct blk_zone, node);
> + if (zone) {
> + spin_lock_irqsave(&zone->lock, flags);
> + if ((zone->start + zone->len) <= sector)
> + goto out;
> + spin_unlock_irqrestore(&zone->lock, flags);
> + zone = NULL;
> + }
> + }
> return BLKPREP_KILL;
> + }
I do not understand the point of this code here to test for the runt
zone. As long as sector is within the device maximum capacity (in 512B
unit), blk_lookup_zone will return the pointer to the zone structure
containing that sector (the RB-tree does not have any constraint
regarding zone size). The only case where NULL would be returned is if
discard is issued super early right after the disk is probed and before
the zone refresh work has completed. We can certainly protect against
that by delaying the discard.
>
> spin_lock_irqsave(&zone->lock, flags);
> -
> if (zone->state == BLK_ZONE_UNKNOWN ||
> zone->state == BLK_ZONE_BUSY) {
> sd_zbc_debug_ratelimit(sdkp,
> -"Discarding zone %zu state %x,
> deferring\n",
> +"Discarding zone %zx state %x,
> deferring\n",
Sector values are usually displayed in decimal. Why use Hex here ? At
least "0x" would be needed to avoid confusion I think.
> zone->start, zone->state);
> ret = BLKPREP_DEFER;
> goto out;
> @@ -406,46 +428,80 @@ int sd_zbc_setup_discard(struct scsi_disk *sdkp, struct
> request *rq,
> if (zone->state == BLK_ZONE_OFFLINE) {
> /* let the drive fail the command */
> sd_zbc_debug_ratelimit(sdkp,
> -"Discarding offline zone %zu\n",
> +"Discarding offline zone %zx\n",
> zone->start);
> goto out;
> }
> -
> - if (!blk_zone_is_smr(zone)) {
> + if (blk_zone_is_cmr(zone)) {
> + use_write_same = true;
> sd_zbc_debug_ratelimit(sdkp,
> -"Discarding %s zone %zu\n",
> -blk_zone_is_cmr(zone) ? "CMR" :
> "unknown",
> +"Discarding CMR zone %zx\n",
> zone->start);
> - ret = BLKPREP_DONE;
> goto out;
> }
Some 10TB host managed disks out there have 1% conventional zone space,
that is 100GB of capacity. When issuing a "reset all", doing a write
same in these zones will take forever... If the user really wants zeroes
in those zones, let it issue a zeroout.
I think that it would a better choice to simply not report
discard_zeroes_data as true and do nothing for conventional zones reset.
> - if (blk_zone_is_empty(zone)) {
> - sd_zbc_debug_ratelimit(sdkp,
> -"Discarding empty zone %zu\n",
> -zone->start);
> - ret = BLKPREP_DONE;
> + if (zone->start != sector || zone->len < nr_sectors) {
> + sd_printk(KERN_ERR, sdkp,
> + "Misaligned RESET WP %zx/%x on zone %zx/%zx\n",
> + sector, nr_sectors, zone->start, zone->len);
> + ret = BLKPREP_KILL;
> goto out;
> }
> -
> - if (zone->start != sector ||
> - zone->len < num_sectors) {
> + /* Protect against Reset WP when more data had been written to the
> + * zone than is being discarded.
> + */
> + wp_offset = zone->wp - zone->start;
> + if (wp_offset > nr_sectors) {
> sd_printk(KERN_ERR, sdkp,
> -
Re: [PATCH v2 2/4] On Discard either do Reset WP or Write Same
On Mon, Aug 22, 2016 at 6:57 PM, Damien Le Moal wrote:
>
> Shaun,
>
> On 8/22/16 13:31, Shaun Tancheff wrote:
> [...]
>> -int sd_zbc_setup_discard(struct scsi_disk *sdkp, struct request *rq,
>> - sector_t sector, unsigned int num_sectors)
>> +int sd_zbc_setup_discard(struct scsi_cmnd *cmd)
>> {
>> - struct blk_zone *zone;
>> + struct request *rq = cmd->request;
>> + struct scsi_device *sdp = cmd->device;
>> + struct scsi_disk *sdkp = scsi_disk(rq->rq_disk);
>> + sector_t sector = blk_rq_pos(rq);
>> + unsigned int nr_sectors = blk_rq_sectors(rq);
>> int ret = BLKPREP_OK;
>> + struct blk_zone *zone;
>> unsigned long flags;
>> + u32 wp_offset;
>> + bool use_write_same = false;
>>
>> zone = blk_lookup_zone(rq->q, sector);
>> - if (!zone)
>> + if (!zone) {
>> + /* Test for a runt zone before giving up */
>> + if (sdp->type != TYPE_ZBC) {
>> + struct request_queue *q = rq->q;
>> + struct rb_node *node;
>> +
>> + node = rb_last(&q->zones);
>> + if (node)
>> + zone = rb_entry(node, struct blk_zone, node);
>> + if (zone) {
>> + spin_lock_irqsave(&zone->lock, flags);
>> + if ((zone->start + zone->len) <= sector)
>> + goto out;
>> + spin_unlock_irqrestore(&zone->lock, flags);
>> + zone = NULL;
>> + }
>> + }
>> return BLKPREP_KILL;
>> + }
>
> I do not understand the point of this code here to test for the runt
> zone. As long as sector is within the device maximum capacity (in 512B
> unit), blk_lookup_zone will return the pointer to the zone structure
> containing that sector (the RB-tree does not have any constraint
> regarding zone size). The only case where NULL would be returned is if
> discard is issued super early right after the disk is probed and before
> the zone refresh work has completed. We can certainly protect against
> that by delaying the discard.
As you can see I am not including Host Managed in the
runt check.
Also you may note that in my patch to get Host Aware working
with the zone cache I do not include the runt zone in the cache.
So as it sits I need this fallback otherwise doing blkdiscard over
the whole device ends in a error, as well as mkfs.f2fs et. al.
>> spin_lock_irqsave(&zone->lock, flags);
>> -
>> if (zone->state == BLK_ZONE_UNKNOWN ||
>> zone->state == BLK_ZONE_BUSY) {
>> sd_zbc_debug_ratelimit(sdkp,
>> -"Discarding zone %zu state %x,
>> deferring\n",
>> +"Discarding zone %zx state %x,
>> deferring\n",
>
> Sector values are usually displayed in decimal. Why use Hex here ? At
> least "0x" would be needed to avoid confusion I think.
Yeah, my brain is lazy about converting very large
numbers to powers of 2. So it's much easier to spot
zone alignment here.
>> zone->start, zone->state);
>> ret = BLKPREP_DEFER;
>> goto out;
>> @@ -406,46 +428,80 @@ int sd_zbc_setup_discard(struct scsi_disk *sdkp,
>> struct request *rq,
>> if (zone->state == BLK_ZONE_OFFLINE) {
>> /* let the drive fail the command */
>> sd_zbc_debug_ratelimit(sdkp,
>> -"Discarding offline zone %zu\n",
>> +"Discarding offline zone %zx\n",
>> zone->start);
>> goto out;
>> }
>> -
>> - if (!blk_zone_is_smr(zone)) {
>> + if (blk_zone_is_cmr(zone)) {
>> + use_write_same = true;
>> sd_zbc_debug_ratelimit(sdkp,
>> -"Discarding %s zone %zu\n",
>> -blk_zone_is_cmr(zone) ? "CMR" :
>> "unknown",
>> +"Discarding CMR zone %zx\n",
>> zone->start);
>> - ret = BLKPREP_DONE;
>> goto out;
>> }
>
> Some 10TB host managed disks out there have 1% conventional zone space,
> that is 100GB of capacity. When issuing a "reset all", doing a write
> same in these zones will take forever... If the user really wants zeroes
> in those zones, let it issue a zeroout.
>
> I think that it would a better choice to simply not report
> discard_zeroes_data as true and do nothing for conventional zones reset.
I think that would be unfortunate for Host Managed but I think it's
the right choice for Host Aware at this time. So either we base
it on disk type or we have some other config flag added to sysfs.
>> - if (blk_zone_is_empty(zone)) {
>> - sd_zbc_debug_ratelimit(sdkp,
>>
Re: [PATCH v2 2/4] On Discard either do Reset WP or Write Same
Shaun,
On 8/23/16 09:22, Shaun Tancheff wrote:
> On Mon, Aug 22, 2016 at 6:57 PM, Damien Le Moal
> wrote:
>>
>> Shaun,
>>
>> On 8/22/16 13:31, Shaun Tancheff wrote:
>> [...]
>>> -int sd_zbc_setup_discard(struct scsi_disk *sdkp, struct request *rq,
>>> - sector_t sector, unsigned int num_sectors)
>>> +int sd_zbc_setup_discard(struct scsi_cmnd *cmd)
>>> {
>>> - struct blk_zone *zone;
>>> + struct request *rq = cmd->request;
>>> + struct scsi_device *sdp = cmd->device;
>>> + struct scsi_disk *sdkp = scsi_disk(rq->rq_disk);
>>> + sector_t sector = blk_rq_pos(rq);
>>> + unsigned int nr_sectors = blk_rq_sectors(rq);
>>> int ret = BLKPREP_OK;
>>> + struct blk_zone *zone;
>>> unsigned long flags;
>>> + u32 wp_offset;
>>> + bool use_write_same = false;
>>>
>>> zone = blk_lookup_zone(rq->q, sector);
>>> - if (!zone)
>>> + if (!zone) {
>>> + /* Test for a runt zone before giving up */
>>> + if (sdp->type != TYPE_ZBC) {
>>> + struct request_queue *q = rq->q;
>>> + struct rb_node *node;
>>> +
>>> + node = rb_last(&q->zones);
>>> + if (node)
>>> + zone = rb_entry(node, struct blk_zone, node);
>>> + if (zone) {
>>> + spin_lock_irqsave(&zone->lock, flags);
>>> + if ((zone->start + zone->len) <= sector)
>>> + goto out;
>>> + spin_unlock_irqrestore(&zone->lock, flags);
>>> + zone = NULL;
>>> + }
>>> + }
>>> return BLKPREP_KILL;
>>> + }
>>
>> I do not understand the point of this code here to test for the runt
>> zone. As long as sector is within the device maximum capacity (in 512B
>> unit), blk_lookup_zone will return the pointer to the zone structure
>> containing that sector (the RB-tree does not have any constraint
>> regarding zone size). The only case where NULL would be returned is if
>> discard is issued super early right after the disk is probed and before
>> the zone refresh work has completed. We can certainly protect against
>> that by delaying the discard.
>
> As you can see I am not including Host Managed in the
> runt check.
Indeed, but having a runt zone could also happen with a host-managed disk.
> Also you may note that in my patch to get Host Aware working
> with the zone cache I do not include the runt zone in the cache.
Why not ? The RB-tree will handle it just fine (the insert and lookup
code as Hannes had them was not relying on a constant zone size).
> So as it sits I need this fallback otherwise doing blkdiscard over
> the whole device ends in a error, as well as mkfs.f2fs et. al.
Got it, but I do not see a problem with including it. I have not checked
the code, but the split of a big discard call into "chunks" should be
already handling the last chunk and make sure that the operation does
not exceed the device capacity (in any case, that's easy to fix in the
sd_zbc_setup_discard code).
>>> zone->start, zone->state);
>>> ret = BLKPREP_DEFER;
>>> goto out;
>>> @@ -406,46 +428,80 @@ int sd_zbc_setup_discard(struct scsi_disk *sdkp,
>>> struct request *rq,
>>> if (zone->state == BLK_ZONE_OFFLINE) {
>>> /* let the drive fail the command */
>>> sd_zbc_debug_ratelimit(sdkp,
>>> -"Discarding offline zone %zu\n",
>>> +"Discarding offline zone %zx\n",
>>> zone->start);
>>> goto out;
>>> }
>>> -
>>> - if (!blk_zone_is_smr(zone)) {
>>> + if (blk_zone_is_cmr(zone)) {
>>> + use_write_same = true;
>>> sd_zbc_debug_ratelimit(sdkp,
>>> -"Discarding %s zone %zu\n",
>>> -blk_zone_is_cmr(zone) ? "CMR" :
>>> "unknown",
>>> +"Discarding CMR zone %zx\n",
>>> zone->start);
>>> - ret = BLKPREP_DONE;
>>> goto out;
>>> }
>>
>> Some 10TB host managed disks out there have 1% conventional zone space,
>> that is 100GB of capacity. When issuing a "reset all", doing a write
>> same in these zones will take forever... If the user really wants zeroes
>> in those zones, let it issue a zeroout.
>>
>> I think that it would a better choice to simply not report
>> discard_zeroes_data as true and do nothing for conventional zones reset.
>
> I think that would be unfortunate for Host Managed but I think it's
> the right choice for Host Aware at this time. So either we base
> it on disk type or we have some other config flag added to sysfs.
I do not see any difference be
Re: [PATCH v2 2/4] On Discard either do Reset WP or Write Same
On Mon, Aug 22, 2016 at 8:25 PM, Damien Le Moal wrote: > > Shaun, > > On 8/23/16 09:22, Shaun Tancheff wrote: >> On Mon, Aug 22, 2016 at 6:57 PM, Damien Le Moal >> wrote: >> Also you may note that in my patch to get Host Aware working >> with the zone cache I do not include the runt zone in the cache. > > Why not ? The RB-tree will handle it just fine (the insert and lookup > code as Hannes had them was not relying on a constant zone size). A good point. I didn't pay too much attention while brining this forward. I think a few of my hacks may be pointless now. I'll try to rework it and get rid of the runt check. >> So as it sits I need this fallback otherwise doing blkdiscard over >> the whole device ends in a error, as well as mkfs.f2fs et. al. > > Got it, but I do not see a problem with including it. I have not checked > the code, but the split of a big discard call into "chunks" should be > already handling the last chunk and make sure that the operation does > not exceed the device capacity (in any case, that's easy to fix in the > sd_zbc_setup_discard code). Yes I agree the split of big discards does handle the last chunk correctly. >>> Some 10TB host managed disks out there have 1% conventional zone space, >>> that is 100GB of capacity. When issuing a "reset all", doing a write >>> same in these zones will take forever... If the user really wants zeroes >>> in those zones, let it issue a zeroout. >>> >>> I think that it would a better choice to simply not report >>> discard_zeroes_data as true and do nothing for conventional zones reset. >> >> I think that would be unfortunate for Host Managed but I think it's >> the right choice for Host Aware at this time. So either we base >> it on disk type or we have some other config flag added to sysfs. > > I do not see any difference between host managed and host aware. Both > define the same behavior for reset, and both end up in a NOP for > conventional zone reset (no data "erasure" required by the standard). > For write pointer zones, reading unwritten LBAs returns the > initialization pattern, with the exception of host-managed disks with > the URSWRZ bit set to 0. But that case is covered in sd.c, so the > behavior is consistent across all models. So why forcing data zeroing > when the standards do not mandate it ? Well you do have point. It appears to be only mkfs and similar tools that are really utilizing discard zeros data at the moment. I did a quick test: mkfs -t ext4 -b 4096 -g 32768 -G 32 \ -E lazy_itable_init=0,lazy_journal_init=0,offset=0,num_backup_sb=0,packed_meta_blocks=1,discard \ -O flex_bg,extent,sparse_super2 - discard zeroes data true - 3 minutess - discard zeroes data false - 6 minutes So for the smaller conventional space on the current HA drive there is some advantage to enabling discard zeroes data. However for a larger conventional space you are correct the overall impact is worse performance. For some reason I had been assuming that some file systems used or relied on discard zeroes data during normal operation. Now that I am looking for that I don't seem to be finding any evidence of it, so aside from mkfs I don't have as good an argument discard zeroes data as I though I did. Regards, Shaun -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
