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[PATCH v6 0/2] Block layer support ZAC/ZBC commands

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  [PATCH v6 0/2] Block layer support ZAC/ZBC commands Shaun Tancheff <shaun@tancheff.com> - 2016-07-29 21:10 +0200
    Re: [PATCH v6 0/2] Block layer support ZAC/ZBC commands Christoph Hellwig <hch@lst.de> - 2016-08-01 11:50 +0200
      Re: [PATCH v6 0/2] Block layer support ZAC/ZBC commands Shaun Tancheff <shaun.tancheff@seagate.com> - 2016-08-01 19:40 +0200
        Re: [PATCH v6 0/2] Block layer support ZAC/ZBC commands Hannes Reinecke <hare@suse.de> - 2016-08-02 17:30 +0200
          Re: [PATCH v6 0/2] Block layer support ZAC/ZBC commands Damien Le Moal <Damien.LeMoal@hgst.com> - 2016-08-03 03:40 +0200
            Re: [PATCH v6 0/2] Block layer support ZAC/ZBC commands Shaun Tancheff <shaun.tancheff@seagate.com> - 2016-08-05 22:40 +0200
              Re: [PATCH v6 0/2] Block layer support ZAC/ZBC commands Hannes Reinecke <hare@suse.de> - 2016-08-09 08:50 +0200
                Re: [PATCH v6 0/2] Block layer support ZAC/ZBC commands Damien Le Moal <Damien.LeMoal@hgst.com> - 2016-08-09 10:20 +0200
                  Re: [PATCH v6 0/2] Block layer support ZAC/ZBC commands Shaun Tancheff <shaun.tancheff@seagate.com> - 2016-08-10 06:00 +0200
                Re: [PATCH v6 0/2] Block layer support ZAC/ZBC commands Shaun Tancheff <shaun.tancheff@seagate.com> - 2016-08-10 05:30 +0200

#1452522 — [PATCH v6 0/2] Block layer support ZAC/ZBC commands

Hi Jens,

This series is based on linus' current tip after the merge of 'for-4.8/core'

As Host Aware drives are becoming available we would like to be able
to make use of such drives. This series is also intended to be suitable
for use by Host Managed drives.

ZAC/ZBC drives add new commands for discovering and working with Zones.

This extends the ZAC/ZBC support up to the block layer allowing direct control
by file systems or device mapper targets. Also by deferring the zone handling
to the authoritative subsystem there is an overall lower memory usage for
holding the active zone information as well as clarifying responsible party
for maintaining the write pointer for each active zone.
By way of example a DM target may have several writes in progress. To sector
(or lba) for those writes will each depend on the previous write. While the
drive's write pointer will be updated as writes are completed the DM target
will be maintaining both where the next write should be scheduled from and 
where the write pointer is based on writes completed w/o errors.
Knowing the drive's zone topology enables DM targets and file systems to
extend their block allocation schemes and issue write pointer resets (or 
discards) that are zone aligned.
A perhaps non-obvious approach is that a conventional drive will 
returns a zone report descriptor with a single large conventional zone.

Patches for util-linux can be found here:
https://github.com/Seagate/ZDM-Device-Mapper/tree/master/patches/util-linux

This patch is available here:
    https://github.com/stancheff/linux/tree/zbc.bio.v6

    git@github.com:stancheff/linux.git zbc.bio.v6

v6:
 - Fix page alloc to include DMA flag for ioctl.
v5:
 - In sd_setup_zone_action_cmnd, remove unused vars and fix switch indent
 - In blk-lib fix documentation
v4:
 - Rebase on linux-next tag next-20160617.
 - Change bio flags to bio op's
 - Dropped ata16 hackery
V3:
 - Rebase on Mike Cristie's separate bio operations
 - Update blkzoned_api.h to include report zones PARTIAL bit.
 - Use zoned report reserved bit for ata-passthrough flag.

V2:
 - Changed bi_rw to op_flags clarify sepeartion of bio op from flags.
 - Fixed memory leak in blkdev_issue_zone_report failing to put_bio().
 - Documented opt in blkdev_issue_zone_report.
 - Moved include/uapi/linux/fs.h changes to patch 3
 - Fixed commit message for first patch in series.

Shaun Tancheff (2):
  Add bio/request flags to issue ZBC/ZAC commands
  Add ioctl to issue ZBC/ZAC commands via block layer

 MAINTAINERS                       |   9 ++
 block/blk-lib.c                   |  95 ++++++++++++++++
 block/ioctl.c                     | 110 +++++++++++++++++++
 drivers/scsi/sd.c                 | 118 ++++++++++++++++++++
 drivers/scsi/sd.h                 |   1 +
 include/linux/bio.h               |   7 +-
 include/linux/blk_types.h         |   6 +-
 include/linux/blkzoned_api.h      |  25 +++++
 include/uapi/linux/Kbuild         |   1 +
 include/uapi/linux/blkzoned_api.h | 220 ++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/fs.h           |   1 +
 11 files changed, 591 insertions(+), 2 deletions(-)
 create mode 100644 include/linux/blkzoned_api.h
 create mode 100644 include/uapi/linux/blkzoned_api.h

-- 
2.8.1

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#1453078

Can you please integrate this with Hannes series so that it uses
his cache of the zone information?

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#1453363

On Mon, Aug 1, 2016 at 4:41 AM, Christoph Hellwig <hch@lst.de> wrote:
>
> Can you please integrate this with Hannes series so that it uses
> his cache of the zone information?

Adding Hannes and Damien to Cc.

Christoph,

I can make a patch the marshal Hannes' RB-Tree into to a block report, that is
quite simple. I can even have the open/close/reset zone commands update the
RB-Tree .. the non-private parts anyway. I would prefer to do this around the
CONFIG_SD_ZBC support, offering the existing type of patch for setups that do
not need the RB-Tree to function with zoned media.

I do still have concerns with the approach which I have shared in smaller
forums but perhaps I have to bring them to this group.

First is the memory consumption. This isn't really much of a concern for large
servers with few drives but I think the embedded NAS market will grumble as
well as the large data pods trying to stuff 300+ drives in a chassis.

As of now the RB-Tree needs to hold ~30000 zones.
sizeof() reports struct blk_zone to use 120 bytes on x86_64. This yields
around 3.5 MB per zoned drive attached.
Which is fine if it is really needed, but most of it is fixed information
and it can be significantly condensed (I have proposed 8 bytes per zone held
in an array as more than adequate). Worse is that the crucial piece of
information, the current wp needed for scheduling the next write, is mostly
out of date because it is updated only after the write completes and zones
being actively written to must work off of the last location / size that was
submitted, not completed. The work around is for that tracking to be handled
in the private_data member. I am not saying that updating the wp on
completing a write isn’t important, I am saying that the bi_end_io hook is
the existing hook that works just fine.

This all tails into domain responsability. With the RB-Tree doing half of the
work and the ‘responsible’ domain handling the active path via private_data
why have the split at all? It seems to be a double work to have second object
tracking the first so that I/O scheduling can function.

Finally is the error handling path when the RB-Tree encounters and error it
attempts to requery the drive topology virtually guaranteeing that the
private_data is now out-of-sync with the RB-Tree. Again this is something
that can be better encapsulated in the bi_end_io to be informed of the
failed I/O and schedule the appropriate recovery (including re-querying the
zone information of the affected zone(s)).

Anyway those are my concerns and why I am still reluctant to drop this line of
support. I have incorporated Hannes changes at various points. Hence the
SCT Write Same to attempt to work around some of the flaws in mapping
discard to reset write pointer.

Thanks and Regards,
Shaun

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-- 
Shaun Tancheff

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#1454745

On 08/01/2016 07:07 PM, Shaun Tancheff wrote:
> On Mon, Aug 1, 2016 at 4:41 AM, Christoph Hellwig <hch@lst.de> wrote:
>>
>> Can you please integrate this with Hannes series so that it uses
>> his cache of the zone information?
> 
> Adding Hannes and Damien to Cc.
> 
> Christoph,
> 
> I can make a patch the marshal Hannes' RB-Tree into to a block report, that is
> quite simple. I can even have the open/close/reset zone commands update the
> RB-Tree .. the non-private parts anyway. I would prefer to do this around the
> CONFIG_SD_ZBC support, offering the existing type of patch for setups that do
> not need the RB-Tree to function with zoned media.
> 
> I do still have concerns with the approach which I have shared in smaller
> forums but perhaps I have to bring them to this group.
> 
> First is the memory consumption. This isn't really much of a concern for large
> servers with few drives but I think the embedded NAS market will grumble as
> well as the large data pods trying to stuff 300+ drives in a chassis.
> 
> As of now the RB-Tree needs to hold ~30000 zones.
> sizeof() reports struct blk_zone to use 120 bytes on x86_64. This yields
> around 3.5 MB per zoned drive attached.
> Which is fine if it is really needed, but most of it is fixed information
> and it can be significantly condensed (I have proposed 8 bytes per zone held
> in an array as more than adequate). Worse is that the crucial piece of
> information, the current wp needed for scheduling the next write, is mostly
> out of date because it is updated only after the write completes and zones
> being actively written to must work off of the last location / size that was
> submitted, not completed. The work around is for that tracking to be handled
> in the private_data member. I am not saying that updating the wp on
> completing a write isn’t important, I am saying that the bi_end_io hook is
> the existing hook that works just fine.
> 
Which _actually_ is not true; with my patches I'll update the write
pointer prior to submit the I/O (on the reasoning that most of the time
I/O will succeed) and re-read the zone information if an I/O failed.
(Which I'll have to do anyway as after an I/O failure the write pointer
status is not clearly defined.)

I have thought about condensing the RB tree information, but then I
figured that for 'real' SMR handling we cannot assume all zones are of
fixed size, and hence we need all the information there.
Any condensing method would assume a given structure of the zones, which
the standard just doesn't provide.
Or am I missing something here?

As for write pointer handling: yes, the write pointer on the zones is
not really useful for upper-level usage.
Where we do need it is to detect I/O which is crossing the write pointer
(eg when doing reads over the entire zone).
As per spec you will be getting an I/O error here, so we need to split
the I/O on the write pointer to get valid results back.

> This all tails into domain responsibility. With the RB-Tree doing half of the
> work and the ‘responsible’ domain handling the active path via private_data
> why have the split at all? It seems to be a double work to have second object
> tracking the first so that I/O scheduling can function.
> 
Tracking the zone states via RB trees is mainly to handly host-managed
drives seamlessly. Without an RB tree we will be subjected to I/O errors
during boot, as eg with new drives we inevitably will try to read beyond
the write pointer, which in turn will generate I/O errors on certain drives.
I do agree that there is no strict need to setup an RB tree for
host-aware drives; I can easily add an attribute/flag to disable RB
trees for those.
However, tracking zone information in the RB tree _dramatically_ speeds
up device initialisation; issuing a blkdev_discard() for the entire
drive will take _ages_ without it.

> Finally is the error handling path when the RB-Tree encounters and error it
> attempts to requery the drive topology virtually guaranteeing that the
> private_data is now out-of-sync with the RB-Tree. Again this is something
> that can be better encapsulated in the bi_end_io to be informed of the
> failed I/O and schedule the appropriate recovery (including re-querying the
> zone information of the affected zone(s)).
> 
Well, if we have an RB tree with write pointers of course we need to
re-read the zone information on failure (and I thought I did that?).
Plus the error information will be propagated via the usual mechanism,
so they need to take care of updating any information in ->private_data.

I'm perfectly fine with integrating your patches for the various
blkdev_XX callouts and associated ioctls; Jens favours that approach,
too, so we should be combining those efforts.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)

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#1455570

Hannes, Shaun,

Let me add some more comments.

> On Aug 2, 2016, at 23:35, Hannes Reinecke <hare@suse.de> wrote:
> 
> On 08/01/2016 07:07 PM, Shaun Tancheff wrote:
>> On Mon, Aug 1, 2016 at 4:41 AM, Christoph Hellwig <hch@lst.de> wrote:
>>> 
>>> Can you please integrate this with Hannes series so that it uses
>>> his cache of the zone information?
>> 
>> Adding Hannes and Damien to Cc.
>> 
>> Christoph,
>> 
>> I can make a patch the marshal Hannes' RB-Tree into to a block report, that is
>> quite simple. I can even have the open/close/reset zone commands update the
>> RB-Tree .. the non-private parts anyway. I would prefer to do this around the
>> CONFIG_SD_ZBC support, offering the existing type of patch for setups that do
>> not need the RB-Tree to function with zoned media.
>> 
>> I do still have concerns with the approach which I have shared in smaller
>> forums but perhaps I have to bring them to this group.
>> 
>> First is the memory consumption. This isn't really much of a concern for large
>> servers with few drives but I think the embedded NAS market will grumble as
>> well as the large data pods trying to stuff 300+ drives in a chassis.
>> 
>> As of now the RB-Tree needs to hold ~30000 zones.
>> sizeof() reports struct blk_zone to use 120 bytes on x86_64. This yields
>> around 3.5 MB per zoned drive attached.
>> Which is fine if it is really needed, but most of it is fixed information
>> and it can be significantly condensed (I have proposed 8 bytes per zone held
>> in an array as more than adequate). Worse is that the crucial piece of
>> information, the current wp needed for scheduling the next write, is mostly
>> out of date because it is updated only after the write completes and zones
>> being actively written to must work off of the last location / size that was
>> submitted, not completed. The work around is for that tracking to be handled
>> in the private_data member. I am not saying that updating the wp on
>> completing a write isn’t important, I am saying that the bi_end_io hook is
>> the existing hook that works just fine.
>> 
> Which _actually_ is not true; with my patches I'll update the write
> pointer prior to submit the I/O (on the reasoning that most of the time
> I/O will succeed) and re-read the zone information if an I/O failed.
> (Which I'll have to do anyway as after an I/O failure the write pointer
> status is not clearly defined.)
> 
> I have thought about condensing the RB tree information, but then I
> figured that for 'real' SMR handling we cannot assume all zones are of
> fixed size, and hence we need all the information there.
> Any condensing method would assume a given structure of the zones, which
> the standard just doesn't provide.
> Or am I missing something here?

Indeed, the standards do not mandate any particular zone configuration,
constant zone size, etc. So writing code so that can be handled is certainly
the right way of doing things. However, if we decide to go forward with
mapping RESET WRITE POINTER command to DISCARD, then at least a constant
zone size (minus the last zone as you said) must be assumed, and that
information can be removed from the entries in the RB tree (as it will be
saved for the sysfs "zone_size" file anyway. Adding a little code to handle
that eventual last runt zone with a different size is not a big problem.

> 
> As for write pointer handling: yes, the write pointer on the zones is
> not really useful for upper-level usage.
> Where we do need it is to detect I/O which is crossing the write pointer
> (eg when doing reads over the entire zone).
> As per spec you will be getting an I/O error here, so we need to split
> the I/O on the write pointer to get valid results back.

To be precise here, the I/O splitting will be handled by the block layer
thanks to the "chunk_sectors" setting. But that relies on a constant zone
size assumption too.

The RB-tree here is most useful for reads over or after the write pointer as
this can have different behavior on different drives (URSWRZ bit). The RB-tree
allows us to hide these differences to upper layers and simplify support at
those levels.

I too agree that the write pointer value is not very useful to upper layers
(e.g. FS). What matters most of the times for these layers is an "allocation
pointer" or "submission pointer" which indicates the LBA to use for the next
BIO submission. That LBA will most of the time be in advance of the zone WP
because of request queing in the block scheduler.
Note that from what we have done already, in many cases, upper layers do not
even need this (e.g. F2FS, btrfs) and work fine without needing *any* 
zone->private_data because that "allocation pointer" information generally
already exists in a different form (e.g. a bit in a bitmap).
For these cases, not having the RB-tree of zones would force a lot
more code to be added to file systems for SMR support.

> 
>> This all tails into domain responsibility. With the RB-Tree doing half of the
>> work and the ‘responsible’ domain handling the active path via private_data
>> why have the split at all? It seems to be a double work to have second object
>> tracking the first so that I/O scheduling can function.
>> 
> Tracking the zone states via RB trees is mainly to handly host-managed
> drives seamlessly. Without an RB tree we will be subjected to I/O errors
> during boot, as eg with new drives we inevitably will try to read beyond
> the write pointer, which in turn will generate I/O errors on certain drives.
> I do agree that there is no strict need to setup an RB tree for
> host-aware drives; I can easily add an attribute/flag to disable RB
> trees for those.
> However, tracking zone information in the RB tree _dramatically_ speeds
> up device initialisation; issuing a blkdev_discard() for the entire
> drive will take _ages_ without it.

And the RB-tree will also be very useful for speeding up report zones
ioctls too. Unless we want those to force an update of the RB-tree information ?

> 
>> Finally is the error handling path when the RB-Tree encounters and error it
>> attempts to requery the drive topology virtually guaranteeing that the
>> private_data is now out-of-sync with the RB-Tree. Again this is something
>> that can be better encapsulated in the bi_end_io to be informed of the
>> failed I/O and schedule the appropriate recovery (including re-querying the
>> zone information of the affected zone(s)).
>> 
> Well, if we have an RB tree with write pointers of course we need to
> re-read the zone information on failure (and I thought I did that?).
> Plus the error information will be propagated via the usual mechanism,
> so they need to take care of updating any information in ->private_data.
> 
> I'm perfectly fine with integrating your patches for the various
> blkdev_XX callouts and associated ioctls; Jens favours that approach,
> too, so we should be combining those efforts.

Can we agree on an interface ?
Summarizing all the discussions we had, I am all in favor of the following:

1) A "zone_size" sysfs attribute to indicate that a drive is zoned:
The already existing device type file can tell us if this is an host
managed disk (type==20) or a host aware disk (type==0). Drive managed
disks could also be detected, but since no information on their zone
configuration can be obtained, lets treat those as regular drives.

2) Add ioctls for zone management:
Report zones (get information from RB tree), reset zone (simple wrapper
to ioctl for block discard), open zone, close zone and finish zone. That
will allow mkfs like tools to get zone information without having to parse
thousands of sysfs files (and can also be integrated in libzbc block backend
driver for a unified interface with the direct SG_IO path for kernels without
the ZBC code enabled).

3) Try to condense the blkzone data structure to save memory:
I think that we can at the very least remove the zone length, and also
may be the per zone spinlock too (a single spinlock and proper state flags can
be used).

Best regards.

------------------------
Damien Le Moal, Ph.D.
Sr. Manager, System Software Group, HGST Research,
HGST, a Western Digital brand
Damien.LeMoal@hgst.com
(+81) 0466-98-3593 (ext. 513593)
1 kirihara-cho, Fujisawa, 
Kanagawa, 252-0888 Japan
www.hgst.com 

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#1457274

On Tue, Aug 2, 2016 at 8:29 PM, Damien Le Moal <Damien.LeMoal@hgst.com> wrote:
> Hannes, Shaun,
>
> Let me add some more comments.
>
>> On Aug 2, 2016, at 23:35, Hannes Reinecke <hare@suse.de> wrote:
>>
>> On 08/01/2016 07:07 PM, Shaun Tancheff wrote:
>>> On Mon, Aug 1, 2016 at 4:41 AM, Christoph Hellwig <hch@lst.de> wrote:
>>>>
>>>> Can you please integrate this with Hannes series so that it uses
>>>> his cache of the zone information?
>>>
>>> Adding Hannes and Damien to Cc.
>>>
>>> Christoph,
>>>
>>> I can make a patch the marshal Hannes' RB-Tree into to a block report, that is
>>> quite simple. I can even have the open/close/reset zone commands update the
>>> RB-Tree .. the non-private parts anyway. I would prefer to do this around the
>>> CONFIG_SD_ZBC support, offering the existing type of patch for setups that do
>>> not need the RB-Tree to function with zoned media.

I have posted patches to integrate with the zone cache, hopefully they
make sense.

>>>
>>> I do still have concerns with the approach which I have shared in smaller
>>> forums but perhaps I have to bring them to this group.
>>>
>>> First is the memory consumption. This isn't really much of a concern for large
>>> servers with few drives but I think the embedded NAS market will grumble as
>>> well as the large data pods trying to stuff 300+ drives in a chassis.
>>>
>>> As of now the RB-Tree needs to hold ~30000 zones.
>>> sizeof() reports struct blk_zone to use 120 bytes on x86_64. This yields
>>> around 3.5 MB per zoned drive attached.
>>> Which is fine if it is really needed, but most of it is fixed information
>>> and it can be significantly condensed (I have proposed 8 bytes per zone held
>>> in an array as more than adequate). Worse is that the crucial piece of
>>> information, the current wp needed for scheduling the next write, is mostly
>>> out of date because it is updated only after the write completes and zones
>>> being actively written to must work off of the last location / size that was
>>> submitted, not completed. The work around is for that tracking to be handled
>>> in the private_data member. I am not saying that updating the wp on
>>> completing a write isn’t important, I am saying that the bi_end_io hook is
>>> the existing hook that works just fine.
>>>
>> Which _actually_ is not true; with my patches I'll update the write
>> pointer prior to submit the I/O (on the reasoning that most of the time
>> I/O will succeed) and re-read the zone information if an I/O failed.
>> (Which I'll have to do anyway as after an I/O failure the write pointer
>> status is not clearly defined.)

Apologies for my mis-characterization.

>> I have thought about condensing the RB tree information, but then I
>> figured that for 'real' SMR handling we cannot assume all zones are of
>> fixed size, and hence we need all the information there.
>> Any condensing method would assume a given structure of the zones, which
>> the standard just doesn't provide.
>> Or am I missing something here?
>
> Indeed, the standards do not mandate any particular zone configuration,
> constant zone size, etc. So writing code so that can be handled is certainly
> the right way of doing things. However, if we decide to go forward with
> mapping RESET WRITE POINTER command to DISCARD, then at least a constant
> zone size (minus the last zone as you said) must be assumed, and that
> information can be removed from the entries in the RB tree (as it will be
> saved for the sysfs "zone_size" file anyway. Adding a little code to handle
> that eventual last runt zone with a different size is not a big problem.

>> As for write pointer handling: yes, the write pointer on the zones is
>> not really useful for upper-level usage.
>> Where we do need it is to detect I/O which is crossing the write pointer
>> (eg when doing reads over the entire zone).
>> As per spec you will be getting an I/O error here, so we need to split
>> the I/O on the write pointer to get valid results back.
>
> To be precise here, the I/O splitting will be handled by the block layer
> thanks to the "chunk_sectors" setting. But that relies on a constant zone
> size assumption too.
>
> The RB-tree here is most useful for reads over or after the write pointer as
> this can have different behavior on different drives (URSWRZ bit). The RB-tree
> allows us to hide these differences to upper layers and simplify support at
> those levels.

It is unfortunate that path was chosen rather than returning Made Up Data.
However I don't think this is a file system or device mapper problem as
neither of those layers attempt to read blocks they have not written
(or discarded).
All I can think of something that probes the drive media for a partition table
or other identification...isn't the conventional space sufficient to cover
those cases?
Anyway you could just handle the error and sense codes [CHECK CONDITION /
ILLEGAL REQUEST / ATTEMPT TO READ INVALID DATA] and return MUD
when URSWRZ is 0. It would have the same effect as using the zone cache
without the possibility of the zone cache being out-of-sync.

> I too agree that the write pointer value is not very useful to upper layers
> (e.g. FS). What matters most of the times for these layers is an "allocation
> pointer" or "submission pointer" which indicates the LBA to use for the next
> BIO submission. That LBA will most of the time be in advance of the zone WP
> because of request queing in the block scheduler.

Which is kind of my point.

> Note that from what we have done already, in many cases, upper layers do not
> even need this (e.g. F2FS, btrfs) and work fine without needing *any*
> zone->private_data because that "allocation pointer" information generally
> already exists in a different form (e.g. a bit in a bitmap).

Agreed. Log structured and copy on write file systems are a natural fit for
these types of drives

> For these cases, not having the RB-tree of zones would force a lot
> more code to be added to file systems for SMR support.

I don't understand how the zone cache (RB-tree) is "helping" F2FS or btrfs.
Certainly any of these could trigger the zone cache to be loaded at mkfs
and/or mount time?

>>> This all tails into domain responsibility. With the RB-Tree doing half of the
>>> work and the ‘responsible’ domain handling the active path via private_data
>>> why have the split at all? It seems to be a double work to have second object
>>> tracking the first so that I/O scheduling can function.
>>>
>> Tracking the zone states via RB trees is mainly to handly host-managed
>> drives seamlessly. Without an RB tree we will be subjected to I/O errors
>> during boot, as eg with new drives we inevitably will try to read beyond
>> the write pointer, which in turn will generate I/O errors on certain drives.

If the zone cache is needed to boot then clearly my objection to reading
in the zone report information on drive attach is unfounded. I was under
the impression that this was not the case.

>> I do agree that there is no strict need to setup an RB tree for
>> host-aware drives; I can easily add an attribute/flag to disable RB
>> trees for those.
>> However, tracking zone information in the RB tree _dramatically_ speeds
>> up device initialisation; issuing a blkdev_discard() for the entire
>> drive will take _ages_ without it.
>
> And the RB-tree will also be very useful for speeding up report zones
> ioctls too. Unless we want those to force an update of the RB-tree information ?

That is debatable. I would tend to argue for both. *If* there must be
a zone cache
then reading from the zone cache is a must. Forcing and update of the zone cache
from the media seems like a reasonable thing to be able to do.

Also the zone report is 'slow' in that there is an overhead for the
report itself but
the number of zones per query can be quite large so 4 or 5 I/Os that
run into the
hundreds if milliseconds to cache the entire drive isn't really unworkable for
something that is used infrequently.

>>> Finally is the error handling path when the RB-Tree encounters and error it
>>> attempts to requery the drive topology virtually guaranteeing that the
>>> private_data is now out-of-sync with the RB-Tree. Again this is something
>>> that can be better encapsulated in the bi_end_io to be informed of the
>>> failed I/O and schedule the appropriate recovery (including re-querying the
>>> zone information of the affected zone(s)).
>>>
>> Well, if we have an RB tree with write pointers of course we need to
>> re-read the zone information on failure (and I thought I did that?).
>> Plus the error information will be propagated via the usual mechanism,
>> so they need to take care of updating any information in ->private_data.
>>
>> I'm perfectly fine with integrating your patches for the various
>> blkdev_XX callouts and associated ioctls; Jens favours that approach,
>> too, so we should be combining those efforts.
>
> Can we agree on an interface ?
> Summarizing all the discussions we had, I am all in favor of the following:
>
> 1) A "zone_size" sysfs attribute to indicate that a drive is zoned:
> The already existing device type file can tell us if this is an host
> managed disk (type==20) or a host aware disk (type==0). Drive managed
> disks could also be detected, but since no information on their zone
> configuration can be obtained, lets treat those as regular drives.

Since disk type == 0 for everything that isn't HM so I would prefer the
sysfs 'zoned' file just report if the drive is HA or HM.

> 2) Add ioctls for zone management:
> Report zones (get information from RB tree), reset zone (simple wrapper
> to ioctl for block discard), open zone, close zone and finish zone. That
> will allow mkfs like tools to get zone information without having to parse
> thousands of sysfs files (and can also be integrated in libzbc block backend
> driver for a unified interface with the direct SG_IO path for kernels without
> the ZBC code enabled).

I can add finish zone ... but I really can't think of a use for it, myself.

> 3) Try to condense the blkzone data structure to save memory:
> I think that we can at the very least remove the zone length, and also
> may be the per zone spinlock too (a single spinlock and proper state flags can
> be used).

I have a variant that is an array of descriptors that roughly mimics the
api from blk-zoned.c that I did a few months ago as an example.
I should be able to update that to the current kernel + patches.

-- 
Shaun Tancheff

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#1458445

On 08/05/2016 10:35 PM, Shaun Tancheff wrote:
> On Tue, Aug 2, 2016 at 8:29 PM, Damien Le Moal <Damien.LeMoal@hgst.com> wrote:
>> Hannes, Shaun,
>>
>> Let me add some more comments.
>>
>>> On Aug 2, 2016, at 23:35, Hannes Reinecke <hare@suse.de> wrote:
>>>
>>> On 08/01/2016 07:07 PM, Shaun Tancheff wrote:
>>>> On Mon, Aug 1, 2016 at 4:41 AM, Christoph Hellwig <hch@lst.de> wrote:
>>>>>
>>>>> Can you please integrate this with Hannes series so that it uses
>>>>> his cache of the zone information?
>>>>
>>>> Adding Hannes and Damien to Cc.
>>>>
>>>> Christoph,
>>>>
>>>> I can make a patch the marshal Hannes' RB-Tree into to a block report, that is
>>>> quite simple. I can even have the open/close/reset zone commands update the
>>>> RB-Tree .. the non-private parts anyway. I would prefer to do this around the
>>>> CONFIG_SD_ZBC support, offering the existing type of patch for setups that do
>>>> not need the RB-Tree to function with zoned media.
> 
> I have posted patches to integrate with the zone cache, hopefully they
> make sense.
> 
[ .. ]
>>> I have thought about condensing the RB tree information, but then I
>>> figured that for 'real' SMR handling we cannot assume all zones are of
>>> fixed size, and hence we need all the information there.
>>> Any condensing method would assume a given structure of the zones, which
>>> the standard just doesn't provide.
>>> Or am I missing something here?
>>
>> Indeed, the standards do not mandate any particular zone configuration,
>> constant zone size, etc. So writing code so that can be handled is certainly
>> the right way of doing things. However, if we decide to go forward with
>> mapping RESET WRITE POINTER command to DISCARD, then at least a constant
>> zone size (minus the last zone as you said) must be assumed, and that
>> information can be removed from the entries in the RB tree (as it will be
>> saved for the sysfs "zone_size" file anyway. Adding a little code to handle
>> that eventual last runt zone with a different size is not a big problem.
> 
>>> As for write pointer handling: yes, the write pointer on the zones is
>>> not really useful for upper-level usage.
>>> Where we do need it is to detect I/O which is crossing the write pointer
>>> (eg when doing reads over the entire zone).
>>> As per spec you will be getting an I/O error here, so we need to split
>>> the I/O on the write pointer to get valid results back.
>>
>> To be precise here, the I/O splitting will be handled by the block layer
>> thanks to the "chunk_sectors" setting. But that relies on a constant zone
>> size assumption too.
>>
>> The RB-tree here is most useful for reads over or after the write pointer as
>> this can have different behavior on different drives (URSWRZ bit). The RB-tree
>> allows us to hide these differences to upper layers and simplify support at
>> those levels.
> 
> It is unfortunate that path was chosen rather than returning Made Up Data.
But how would you return made up data without knowing that you _have_ to
generate some?
Of course it's trivial to generate made up data once an I/O error
occurred, but that's too late as the I/O error already happened.

The general idea behind this is that I _really_ do want to avoid
triggering an I/O error on initial access. This kind of thing really
tends to freak out users (connect a new drive and getting I/O errors;
not the best user experience ...)

> However I don't think this is a file system or device mapper problem as
> neither of those layers attempt to read blocks they have not written
> (or discarded).
> All I can think of something that probes the drive media for a partition table
> or other identification...isn't the conventional space sufficient to cover
> those cases?
Upon device scan the kernel will attempt to read the partition tables,
which consists of reading the first few megabytes and the last sector
(for GPT shadow partition tables).
And depending on the driver manufacturer you might or might not have
enough conventional space at the right locations.

> Anyway you could just handle the error and sense codes [CHECK CONDITION /
> ILLEGAL REQUEST / ATTEMPT TO READ INVALID DATA] and return MUD
> when URSWRZ is 0. It would have the same effect as using the zone cache
> without the possibility of the zone cache being out-of-sync.
> 
Yes, but then we would already have registered an I/O error.
And as indicated above, I really do _not_ want to handle all the
customer calls for supposed faulty new SMR drives.

>> I too agree that the write pointer value is not very useful to upper layers
>> (e.g. FS). What matters most of the times for these layers is an "allocation
>> pointer" or "submission pointer" which indicates the LBA to use for the next
>> BIO submission. That LBA will most of the time be in advance of the zone WP
>> because of request queing in the block scheduler.
> 
> Which is kind of my point.
> 
>> Note that from what we have done already, in many cases, upper layers do not
>> even need this (e.g. F2FS, btrfs) and work fine without needing *any*
>> zone->private_data because that "allocation pointer" information generally
>> already exists in a different form (e.g. a bit in a bitmap).
> 
> Agreed. Log structured and copy on write file systems are a natural fit for
> these types of drives
> 
>> For these cases, not having the RB-tree of zones would force a lot
>> more code to be added to file systems for SMR support.
> 
> I don't understand how the zone cache (RB-tree) is "helping" F2FS or btrfs.
> Certainly any of these could trigger the zone cache to be loaded at mkfs
> and/or mount time?
> 
>>>> This all tails into domain responsibility. With the RB-Tree doing half of the
>>>> work and the ‘responsible’ domain handling the active path via private_data
>>>> why have the split at all? It seems to be a double work to have second object
>>>> tracking the first so that I/O scheduling can function.
>>>>
>>> Tracking the zone states via RB trees is mainly to handly host-managed
>>> drives seamlessly. Without an RB tree we will be subjected to I/O errors
>>> during boot, as eg with new drives we inevitably will try to read beyond
>>> the write pointer, which in turn will generate I/O errors on certain drives.
> 
> If the zone cache is needed to boot then clearly my objection to reading
> in the zone report information on drive attach is unfounded. I was under
> the impression that this was not the case.
> 
>>> I do agree that there is no strict need to setup an RB tree for
>>> host-aware drives; I can easily add an attribute/flag to disable RB
>>> trees for those.
>>> However, tracking zone information in the RB tree _dramatically_ speeds
>>> up device initialisation; issuing a blkdev_discard() for the entire
>>> drive will take _ages_ without it.
>>
>> And the RB-tree will also be very useful for speeding up report zones
>> ioctls too. Unless we want those to force an update of the RB-tree information ?
> 
> That is debatable. I would tend to argue for both. *If* there must be
> a zone cache then reading from the zone cache is a must. Forcing and
> update of the zone cache from the media seems like a reasonable thing
> to be able to do.
> 
> Also the zone report is 'slow' in that there is an overhead for the
> report itself but
> the number of zones per query can be quite large so 4 or 5 I/Os that
> run into the
> hundreds if milliseconds to cache the entire drive isn't really unworkable for
> something that is used infrequently.
> 
No, surely not.
But one of the _big_ advantages for the RB tree is blkdev_discard().
Without the RB tree any mkfs program will issue a 'discard' for every
sector. We will be able to coalesce those into one discard per zone, but
we still need to issue one for _every_ zone.
Which is (as indicated) really slow, and easily takes several minutes.
With the RB tree we can short-circuit discards to empty zones, and speed
up processing time dramatically.
Sure we could be moving the logic into mkfs and friends, but that would
require us to change the programs and agree on a library (libzbc?) which
should be handling that.

>>>> Finally is the error handling path when the RB-Tree encounters and error it
>>>> attempts to requery the drive topology virtually guaranteeing that the
>>>> private_data is now out-of-sync with the RB-Tree. Again this is something
>>>> that can be better encapsulated in the bi_end_io to be informed of the
>>>> failed I/O and schedule the appropriate recovery (including re-querying the
>>>> zone information of the affected zone(s)).
>>>>
>>> Well, if we have an RB tree with write pointers of course we need to
>>> re-read the zone information on failure (and I thought I did that?).
>>> Plus the error information will be propagated via the usual mechanism,
>>> so they need to take care of updating any information in ->private_data.
>>>
>>> I'm perfectly fine with integrating your patches for the various
>>> blkdev_XX callouts and associated ioctls; Jens favours that approach,
>>> too, so we should be combining those efforts.
>>
>> Can we agree on an interface ?
>> Summarizing all the discussions we had, I am all in favor of the following:
>>
>> 1) A "zone_size" sysfs attribute to indicate that a drive is zoned:
>> The already existing device type file can tell us if this is an host
>> managed disk (type==20) or a host aware disk (type==0). Drive managed
>> disks could also be detected, but since no information on their zone
>> configuration can be obtained, lets treat those as regular drives.
> 
> Since disk type == 0 for everything that isn't HM so I would prefer the
> sysfs 'zoned' file just report if the drive is HA or HM.
> 
Okay. So let's put in the 'zoned' attribute the device type:
'host-managed', 'host-aware', or 'device managed'.

>> 2) Add ioctls for zone management:
>> Report zones (get information from RB tree), reset zone (simple wrapper
>> to ioctl for block discard), open zone, close zone and finish zone. That
>> will allow mkfs like tools to get zone information without having to parse
>> thousands of sysfs files (and can also be integrated in libzbc block backend
>> driver for a unified interface with the direct SG_IO path for kernels without
>> the ZBC code enabled).
> 
> I can add finish zone ... but I really can't think of a use for it, myself.
> 
Which is not the point. The standard defines this, so clearly someone
found it a reasonable addendum. So let's add this for completeness.

>> 3) Try to condense the blkzone data structure to save memory:
>> I think that we can at the very least remove the zone length, and also
>> may be the per zone spinlock too (a single spinlock and proper state flags can
>> be used).
> 
> I have a variant that is an array of descriptors that roughly mimics the
> api from blk-zoned.c that I did a few months ago as an example.
> I should be able to update that to the current kernel + patches.
> 
Okay. If we restrict the in-kernel SMR drive handling to devices with
identical zone sizes of course we can remove the zone length.
And we can do away with the per-zone spinlock and use a global one instead.

I will be updating my patchset accordingly.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)

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#1458487

Hannes,

> On Aug 9, 2016, at 15:47, Hannes Reinecke <hare@suse.de> wrote:
[...]
>>> 
>>> Can we agree on an interface ?
>>> Summarizing all the discussions we had, I am all in favor of the following:
>>> 
>>> 1) A "zone_size" sysfs attribute to indicate that a drive is zoned:
>>> The already existing device type file can tell us if this is an host
>>> managed disk (type==20) or a host aware disk (type==0). Drive managed
>>> disks could also be detected, but since no information on their zone
>>> configuration can be obtained, lets treat those as regular drives.
>> 
>> Since disk type == 0 for everything that isn't HM so I would prefer the
>> sysfs 'zoned' file just report if the drive is HA or HM.
>> 
> Okay. So let's put in the 'zoned' attribute the device type:
> 'host-managed', 'host-aware', or 'device managed'.

I hacked your patches and simply put a "0" or "1" in the sysfs zoned file.
Any drive that has ZBC/ZAC command support gets a "1", "0" for everything
else. This means that drive managed models are not exposed as zoned block
devices. For HM vs HA differentiation, an application can look at the
device type file since it is already present.

We could indeed set the "zoned" file to the device type, but HM drives and
regular drives will both have "0" in it, so no differentiation possible.
The other choice could be the "zoned" bits defined by ZBC, but these
do not define a value for host managed drives, and the drive managed value
being not "0" could be confusing too. So I settled for a simple 0/1 boolean.

> 
>>> 2) Add ioctls for zone management:
>>> Report zones (get information from RB tree), reset zone (simple wrapper
>>> to ioctl for block discard), open zone, close zone and finish zone. That
>>> will allow mkfs like tools to get zone information without having to parse
>>> thousands of sysfs files (and can also be integrated in libzbc block backend
>>> driver for a unified interface with the direct SG_IO path for kernels without
>>> the ZBC code enabled).
>> 
>> I can add finish zone ... but I really can't think of a use for it, myself.
>> 
> Which is not the point. The standard defines this, so clearly someone
> found it a reasonable addendum. So let's add this for completeness.

Done: I hacked Shaun ioctl code and added finish zone too. The
difference with Shaun initial code is that the ioctl are propagated down to
the driver (__blkdev_driver_ioctl -> sd_ioctl) so that there is no need for
BIO request definition for the zone operations. So a lot less code added.
The ioctls do not mimic exactly the ZBC standard. For instance, there is no
reporting options for report zones, nor is the "all" bit supported for open,
close or finish zone commands. But the information provided on zones is complete
and maps to the standard definitions.

I also added a reset_wp ioctl for completeness, but this one simply calls
blkdev_issue_discard internally, so it is in fact equivalent to the BLKDISCARD
ioctl call with a range exactly aligned on a zone.

> 
>>> 3) Try to condense the blkzone data structure to save memory:
>>> I think that we can at the very least remove the zone length, and also
>>> may be the per zone spinlock too (a single spinlock and proper state flags can
>>> be used).
>> 
>> I have a variant that is an array of descriptors that roughly mimics the
>> api from blk-zoned.c that I did a few months ago as an example.
>> I should be able to update that to the current kernel + patches.
>> 
> Okay. If we restrict the in-kernel SMR drive handling to devices with
> identical zone sizes of course we can remove the zone length.
> And we can do away with the per-zone spinlock and use a global one instead.

Did that too. The blk_zone struct is now exactly 64B. I removed the per zone
spinlock and replaced it with a flag so that zones can still be locked
independently using wait_on_bit_lock & friends (I added the functions
blk_zone_lock, blk_zone_trylock and blk_zone_unlock to do that). This per zone
locking comes in handy to implement the ioctls code without stalling the command
queue for read, writes and discard on different zones.

I however kept the zone length in the structure. The reason for doing so is that
this allows supporting drives with non-constant zone sizes, albeit with a more
limited interface since in such case the device chunk_sectors is not set (that
is how a user or application can detect that the zones are not constant size).
For these drives, the block layer may happily merge BIOs across zone boundaries
and the discard code will not split and align calls on the zones. But upper layers
(an FS or a device mapper) can still do all this by themselves if they want/can
support non-constant zone sizes.

The only exception is drives like the Seagate one with only the last zone of a
different size. This case is handled exactly as if all zones are the same size
simply because any operation on the last smaller zone will naturally align as
the checks of operation size against the drive capacity will do the right things.

The ioctls work for all cases (drive with constant zone size or not). This is again
to allow supporting eventual weird drives at application level. I integrated all
these ioctl into libzbc block device backend driver and everything is fine. Can't
tell the difference with direct-to-drive SG_IO accesses. But unlike these, the zone
ioctls keep the zone information RB-tree cache up to date.

> 
> I will be updating my patchset accordingly.

I need to cleanup my code and rebase on top of 4.8-rc1. Let me do this and I will send
everything for review. If you have any comment on the above, please let me know and
I will be happy to incorporate changes.

Best regards.


------------------------
Damien Le Moal, Ph.D.
Sr. Manager, System Software Group, HGST Research,
HGST, a Western Digital brand
Damien.LeMoal@hgst.com
(+81) 0466-98-3593 (ext. 513593)
1 kirihara-cho, Fujisawa, 
Kanagawa, 252-0888 Japan
www.hgst.com 

Western Digital Corporation (and its subsidiaries) E-mail Confidentiality Notice & Disclaimer:

This e-mail and any files transmitted with it may contain confidential or legally privileged information of WDC and/or its affiliates, and are intended solely for the use of the individual or entity to which they are addressed. If you are not the intended recipient, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it, is prohibited. If you have received this e-mail in error, please notify the sender immediately and delete the e-mail in its entirety from your system.

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#1459276

On Tue, Aug 9, 2016 at 3:09 AM, Damien Le Moal <Damien.LeMoal@hgst.com> wrote:
>> On Aug 9, 2016, at 15:47, Hannes Reinecke <hare@suse.de> wrote:

[trim]

>>> Since disk type == 0 for everything that isn't HM so I would prefer the
>>> sysfs 'zoned' file just report if the drive is HA or HM.
>>>
>> Okay. So let's put in the 'zoned' attribute the device type:
>> 'host-managed', 'host-aware', or 'device managed'.
>
> I hacked your patches and simply put a "0" or "1" in the sysfs zoned file.
> Any drive that has ZBC/ZAC command support gets a "1", "0" for everything
> else. This means that drive managed models are not exposed as zoned block
> devices. For HM vs HA differentiation, an application can look at the
> device type file since it is already present.
>
> We could indeed set the "zoned" file to the device type, but HM drives and
> regular drives will both have "0" in it, so no differentiation possible.
> The other choice could be the "zoned" bits defined by ZBC, but these
> do not define a value for host managed drives, and the drive managed value
> being not "0" could be confusing too. So I settled for a simple 0/1 boolean.

This seems good to me.

>>>> 2) Add ioctls for zone management:
>>>> Report zones (get information from RB tree), reset zone (simple wrapper
>>>> to ioctl for block discard), open zone, close zone and finish zone. That
>>>> will allow mkfs like tools to get zone information without having to parse
>>>> thousands of sysfs files (and can also be integrated in libzbc block backend
>>>> driver for a unified interface with the direct SG_IO path for kernels without
>>>> the ZBC code enabled).
>>>
>>> I can add finish zone ... but I really can't think of a use for it, myself.
>>>
>> Which is not the point. The standard defines this, so clearly someone
>> found it a reasonable addendum. So let's add this for completeness.

Agreed.

> Done: I hacked Shaun ioctl code and added finish zone too. The
> difference with Shaun initial code is that the ioctl are propagated down to
> the driver (__blkdev_driver_ioctl -> sd_ioctl) so that there is no need for
> BIO request definition for the zone operations. So a lot less code added.

The purpose of the BIO flags is not to enable the ioctls so much as
the other way round. Creating BIO op's is to enable issuing ZBC
commands from device mapper targets and file systems without some
heinous ioctl hacks.
Making the resulting block layer interfaces available via ioctls is just a
reasonable way to exercise the code ... or that was my intent.

> The ioctls do not mimic exactly the ZBC standard. For instance, there is no
> reporting options for report zones, nor is the "all" bit supported for open,
> close or finish zone commands. But the information provided on zones is complete
> and maps to the standard definitions.

For the reporting options I have planned to reuse the stream_id in
struct bio when that is formalized. There are certainly other places in
struct bio to stuff a few extra bits ...

As far as the all bit ... this is being handled by all the zone action
commands. Just pass a sector of ~0ul and it's handled in sd.c by
sd_setup_zone_action_cmnd().

Apologies as apparently my documentation here is lacking :-(

> I also added a reset_wp ioctl for completeness, but this one simply calls
> blkdev_issue_discard internally, so it is in fact equivalent to the BLKDISCARD
> ioctl call with a range exactly aligned on a zone.

I'm confused as my patch set includes a Reset WP (BLKRESETZONE) that
creates a REQ_OP_ZONE_RESET .. same as open and close. My
expectation being that BLKDISCARD doesn't really need yet another alias.

[trim]

> Did that too. The blk_zone struct is now exactly 64B. I removed the per zone

Thanks .. being a cache line is harder to whinge about...

> spinlock and replaced it with a flag so that zones can still be locked
> independently using wait_on_bit_lock & friends (I added the functions
> blk_zone_lock, blk_zone_trylock and blk_zone_unlock to do that). This per zone
> locking comes in handy to implement the ioctls code without stalling the command
> queue for read, writes and discard on different zones.
>
> I however kept the zone length in the structure. The reason for doing so is that
> this allows supporting drives with non-constant zone sizes, albeit with a more
> limited interface since in such case the device chunk_sectors is not set (that
> is how a user or application can detect that the zones are not constant size).
> For these drives, the block layer may happily merge BIOs across zone boundaries
> and the discard code will not split and align calls on the zones. But upper layers
> (an FS or a device mapper) can still do all this by themselves if they want/can
> support non-constant zone sizes.
>
> The only exception is drives like the Seagate one with only the last zone of a
> different size. This case is handled exactly as if all zones are the same size
> simply because any operation on the last smaller zone will naturally align as
> the checks of operation size against the drive capacity will do the right things.
>
> The ioctls work for all cases (drive with constant zone size or not). This is again
> to allow supporting eventual weird drives at application level. I integrated all
> these ioctl into libzbc block device backend driver and everything is fine. Can't
> tell the difference with direct-to-drive SG_IO accesses. But unlike these, the zone
> ioctls keep the zone information RB-tree cache up to date.
>
>>
>> I will be updating my patchset accordingly.
>
> I need to cleanup my code and rebase on top of 4.8-rc1. Let me do this and I will send
> everything for review. If you have any comment on the above, please let me know and
> I will be happy to incorporate changes.
>
> Best regards.
>
>
> ------------------------
> Damien Le Moal, Ph.D.
> Sr. Manager, System Software Group, HGST Research,
> HGST, a Western Digital brand
> Damien.LeMoal@hgst.com
> (+81) 0466-98-3593 (ext. 513593)
> 1 kirihara-cho, Fujisawa,
> Kanagawa, 252-0888 Japan
> www.hgst.com
>
> Western Digital Corporation (and its subsidiaries) E-mail Confidentiality Notice & Disclaimer:
>
> This e-mail and any files transmitted with it may contain confidential or legally privileged information of WDC and/or its affiliates, and are intended solely for the use of the individual or entity to which they are addressed. If you are not the intended recipient, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it, is prohibited. If you have received this e-mail in error, please notify the sender immediately and delete the e-mail in its entirety from your system.
>



-- 
Shaun Tancheff

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#1459262

On Tue, Aug 9, 2016 at 1:47 AM, Hannes Reinecke <hare@suse.de> wrote:
> On 08/05/2016 10:35 PM, Shaun Tancheff wrote:
>> On Tue, Aug 2, 2016 at 8:29 PM, Damien Le Moal <Damien.LeMoal@hgst.com> wrote:
>>>> On Aug 2, 2016, at 23:35, Hannes Reinecke <hare@suse.de> wrote:
>>>> On 08/01/2016 07:07 PM, Shaun Tancheff wrote:
>>>>> On Mon, Aug 1, 2016 at 4:41 AM, Christoph Hellwig <hch@lst.de> wrote:

[trim]
>> Also the zone report is 'slow' in that there is an overhead for the
>> report itself but
>> the number of zones per query can be quite large so 4 or 5 I/Os that
>> run into the
>> hundreds if milliseconds to cache the entire drive isn't really unworkable for
>> something that is used infrequently.
>>
> No, surely not.
> But one of the _big_ advantages for the RB tree is blkdev_discard().
> Without the RB tree any mkfs program will issue a 'discard' for every
> sector. We will be able to coalesce those into one discard per zone, but
> we still need to issue one for _every_ zone.
> Which is (as indicated) really slow, and easily takes several minutes.
> With the RB tree we can short-circuit discards to empty zones, and speed
> up processing time dramatically.
> Sure we could be moving the logic into mkfs and friends, but that would
> require us to change the programs and agree on a library (libzbc?) which
> should be handling that.

Adding an additional library dependency seems overkill for a program
that is already doing ioctls and raw block I/O ... but I would leave that
up to each file system. As it sits issuing the ioctl and walking the array
of data returned [see blkreport.c] is already quite trivial.

I believe the goal here is for F2FS, and perhaps NILFS? to "just
work" with the DISCARD to Reset WP and zone cache in place.

Still quite skeptical about other common file systems
"just working" without their respective mkfs et. al. being
zone aware and handling the topology of the media at mkfs time.
Perhaps there is something I am unaware of?

[trim]

>> I can add finish zone ... but I really can't think of a use for it, myself.
>>
> Which is not the point. The standard defines this, so clearly someone
> found it a reasonable addendum. So let's add this for completeness.

Agreed and queued for the next version.

Regards,
Shaun

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