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From: Damien Le Moal <Damien.LeMoal@wdc.com>
To: Kanchan Joshi <firstname.lastname@example.org>
Cc: "email@example.com" <firstname.lastname@example.org>,
Jens Axboe <email@example.com>,
Pavel Begunkov <firstname.lastname@example.org>,
Kanchan Joshi <email@example.com>,
Matthew Wilcox <firstname.lastname@example.org>,
SelvaKumar S <email@example.com>,
Nitesh Shetty <firstname.lastname@example.org>,
Javier Gonzalez <email@example.com>,
Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
Naohiro Aota <Naohiro.Aota@wdc.com>
Subject: Re: [PATCH v4 6/6] io_uring: add support for zone-append
Date: Tue, 29 Sep 2020 01:24:02 +0000 [thread overview]
Message-ID: <CY4PR04MB3751BFF86D1F7F1D22A143E6E7320@CY4PR04MB3751.namprd04.prod.outlook.com> (raw)
On 2020/09/29 3:58, Kanchan Joshi wrote:
> ZoneFS is better when it is about dealing at single-zone granularity,
> and direct-block seems better when it is about grouping zones (in
> various ways including striping). The latter case (i.e. grouping
> zones) requires more involved mapping, and I agree that it can be left
> to application (for both ZoneFS and raw-block backends).
> But when an application tries that on ZoneFS, apart from mapping there
> would be additional cost of indirection/fd-management (due to
There is no indirection in zonefs. fd-to-struct file/inode conversion is very
fast and happens for every system call anyway, regardless of what the fd
represents. So I really do not understand what your worry is here. If you are
worried about overhead/performance, then please show numbers. If something is
wrong, we can work on fixing it.
> And if new features (zone-append for now) are available only on
> ZoneFS, it forces application to use something that maynot be most
> optimal for its need.
"may" is not enough to convince me...
> Coming to the original problem of plumbing append - I think divergence
> started because RWF_APPEND did not have any meaning for block device.
> Did I miss any other reason?
> How about write-anywhere semantics (RWF_RELAXED_WRITE or
> RWF_ANONYMOUS_WRITE flag) on block-dev.
"write-anywhere" ? What do you mean ? That is not possible on zoned devices,
even with zone append, since you at least need to guarantee that zones have
enough unwritten space to accept an append command.
> Zone-append works a lot like write-anywhere on block-dev (or on any
> other file that combines multiple-zones, in non-sequential fashion).
That is an over-simplification that is not helpful at all. Zone append is not
"write anywhere" at all. And "write anywhere" is not a concept that exist on
regular block devices anyway. Writes only go to the offset that the user
decided, through lseek(), pwrite() or aio->aio_offset. It is not like the block
layer decides where the writes land. The same constraint applies to zone append:
the user decide the target zone. That is not "anywhere". Please be precise with
wording and implied/desired semantic. Narrow down the scope of your concept
names for clarity.
And talking about "file that combines multiple-zones" would mean that we are now
back in FS land, not raw block device file accesses anymore. So which one are we
talking about ? It looks like you are confusing what the application does and
how it uses whatever usable interface to the device with what that interface
actually is. It is very confusing.
>>> Also it seems difficult (compared to block dev) to fit simple-copy TP
>>> in ZoneFS. The new
>>> command needs: one NVMe drive, list of source LBAs and one destination
>>> LBA. In ZoneFS, we would deal with N+1 file-descriptors (N source zone
>>> file, and one destination zone file) for that. While with block
>>> interface, we do not need more than one file-descriptor representing
>>> the entire device. With more zone-files, we face open/close overhead too.
>> Are you expecting simple-copy to allow requests that are not zone aligned ? I do
>> not think that will ever happen. Otherwise, the gotcha cases for it would be far
>> too numerous. Simple-copy is essentially an optimized regular write command.
>> Similarly to that command, it will not allow copies over zone boundaries and
>> will need the destination LBA to be aligned to the destination zone WP. I have
>> not checked the TP though and given the NVMe NDA, I will stop the discussion here.
> TP is ratified, if that is the problem you are referring to.
Ah. Yes. Got confused with ZRWA. Simple-copy is a different story anyway. Let's
not mix it into zone append user interface please.
>> filesend() could be used as the interface for simple-copy. Implementing that in
>> zonefs would not be that hard. What is your plan for simple-copy interface for
>> raw block device ? An ioctl ? filesend() too ? As as with any other user level
>> API, we should not be restricted to a particular device type if we can avoid it,
>> so in-kernel emulation of the feature is needed for devices that do not have
>> simple-copy or scsi extended copy. filesend() seems to me like the best choice
>> since all of that is already implemented there.
> At this moment, ioctl as sync and io-uring for async. sendfile() and
> copy_file_range() takes two fds....with that we can represent copy
> from one source zone to another zone.
> But it does not fit to represent larger copy (from N source zones to
> one destination zone).
nvme passthrough ? If that does not fit your use case, then think of an
interface, its definition/semantic and propose it. But again, use a different
thread. This is mixing up zone-append and simple copy, which I do not think are
> Not sure if I am clear, perhaps sending RFC would be better for
> discussion on simple-copy.
Separate this discussion from zone append please. Mixing up 2 problems in one
thread is not helpful to make progress.
Damien Le Moal
Western Digital Research
next prev parent reply other threads:[~2020-09-29 1:24 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20200724155244epcas5p2902f57e36e490ee8772da19aa9408cdc@epcas5p2.samsung.com>
2020-07-24 15:49 ` [PATCH v4 0/6] zone-append support in io-uring and aio Kanchan Joshi
[not found] ` <CGME20200724155258epcas5p1a75b926950a18cd1e6c8e7a047e6c589@epcas5p1.samsung.com>
2020-07-24 15:49 ` [PATCH v4 1/6] fs: introduce FMODE_ZONE_APPEND and IOCB_ZONE_APPEND Kanchan Joshi
2020-07-24 16:34 ` Jens Axboe
2020-07-26 15:18 ` Christoph Hellwig
2020-07-28 1:49 ` Matthew Wilcox
2020-07-28 7:26 ` Christoph Hellwig
[not found] ` <CGME20200724155324epcas5p18e1d3b4402d1e4a8eca87d0b56a3fa9b@epcas5p1.samsung.com>
2020-07-24 15:49 ` [PATCH v4 2/6] fs: change ki_complete interface to support 64bit ret2 Kanchan Joshi
2020-07-26 15:18 ` Christoph Hellwig
[not found] ` <CGME20200724155329epcas5p345ba6bad0b8fe18056bb4bcd26c10019@epcas5p3.samsung.com>
2020-07-24 15:49 ` [PATCH v4 3/6] uio: return status with iov truncation Kanchan Joshi
[not found] ` <CGME20200724155341epcas5p15bfc55927f2abb60f19784270fe8e377@epcas5p1.samsung.com>
2020-07-24 15:49 ` [PATCH v4 4/6] block: add zone append handling for direct I/O path Kanchan Joshi
2020-07-26 15:19 ` Christoph Hellwig
[not found] ` <CGME20200724155346epcas5p2cfb383fe9904a45280c6145f4c13e1b4@epcas5p2.samsung.com>
2020-07-24 15:49 ` [PATCH v4 5/6] block: enable zone-append for iov_iter of bvec type Kanchan Joshi
2020-07-26 15:20 ` Christoph Hellwig
[not found] ` <CGME20200724155350epcas5p3b8f1d59eda7f8fbb38c828f692d42fd6@epcas5p3.samsung.com>
2020-07-24 15:49 ` [PATCH v4 6/6] io_uring: add support for zone-append Kanchan Joshi
2020-07-24 16:29 ` Jens Axboe
2020-07-27 19:16 ` Kanchan Joshi
2020-07-27 20:34 ` Jens Axboe
2020-07-30 16:08 ` Pavel Begunkov
2020-07-30 16:13 ` Jens Axboe
2020-07-30 16:26 ` Pavel Begunkov
2020-07-30 17:16 ` Jens Axboe
2020-07-30 17:38 ` Pavel Begunkov
2020-07-30 17:51 ` Kanchan Joshi
2020-07-30 17:54 ` Jens Axboe
2020-07-30 18:25 ` Kanchan Joshi
2020-07-31 6:42 ` Damien Le Moal
2020-07-31 6:45 ` hch
2020-07-31 6:59 ` Damien Le Moal
2020-07-31 7:58 ` Kanchan Joshi
2020-07-31 8:14 ` Damien Le Moal
2020-07-31 9:14 ` hch
2020-07-31 9:34 ` Damien Le Moal
2020-07-31 9:41 ` hch
2020-07-31 10:16 ` Damien Le Moal
2020-07-31 12:51 ` hch
2020-07-31 13:08 ` hch
2020-07-31 15:07 ` Kanchan Joshi
2020-08-05 7:35 ` Damien Le Moal
2020-08-14 8:14 ` hch
2020-08-14 8:27 ` Damien Le Moal
2020-08-14 12:04 ` hch
2020-08-14 12:20 ` Damien Le Moal
2020-09-07 7:01 ` Kanchan Joshi
2020-09-08 15:18 ` hch
2020-09-24 17:19 ` Kanchan Joshi
2020-09-25 2:52 ` Damien Le Moal
2020-09-28 18:58 ` Kanchan Joshi
2020-09-29 1:24 ` Damien Le Moal [this message]
2020-09-29 18:49 ` Kanchan Joshi
2020-07-31 9:38 ` Kanchan Joshi
2020-07-31 7:08 ` Kanchan Joshi
2020-07-30 15:57 ` Pavel Begunkov
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