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Tue, 29 Sep 2020 01:24:02 +0000 From: Damien Le Moal To: Kanchan Joshi CC: "hch@infradead.org" , Jens Axboe , Pavel Begunkov , Kanchan Joshi , "viro@zeniv.linux.org.uk" , "bcrl@kvack.org" , Matthew Wilcox , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-api@vger.kernel.org" , SelvaKumar S , Nitesh Shetty , Javier Gonzalez , Johannes Thumshirn , Naohiro Aota Subject: Re: [PATCH v4 6/6] io_uring: add support for zone-append Thread-Topic: [PATCH v4 6/6] io_uring: add support for zone-append Thread-Index: AQHWYdbcc0q15qREKECGO7brHi6zEg== Date: Tue, 29 Sep 2020 01:24:02 +0000 Message-ID: References: <20200731091416.GA29634@infradead.org> <20200731094135.GA4104@infradead.org> <20200731125110.GA11500@infradead.org> <20200814081411.GA16943@infradead.org> <20200908151801.GA16742@infradead.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: gmail.com; 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x-ms-exchange-antispam-messagedata: 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 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: CY4PR04MB3751.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 4c516681-1b90-415a-5ea3-08d864165980 X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Sep 2020 01:24:02.2880 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: JAV7ULBYyoo6bnUUzudpgsKRMmGDXB1nBiBZyHnmXVallE4qNBykPWhBS7D+TltUmMdi6IU481gM43vIvWq3kw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR04MB0567 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/09/29 3:58, Kanchan Joshi wrote:=0A= [...]=0A= > ZoneFS is better when it is about dealing at single-zone granularity,=0A= > and direct-block seems better when it is about grouping zones (in=0A= > various ways including striping). The latter case (i.e. grouping=0A= > zones) requires more involved mapping, and I agree that it can be left=0A= > to application (for both ZoneFS and raw-block backends).=0A= > But when an application tries that on ZoneFS, apart from mapping there=0A= > would be additional cost of indirection/fd-management (due to=0A= > file-on-files).=0A= =0A= There is no indirection in zonefs. fd-to-struct file/inode conversion is ve= ry=0A= fast and happens for every system call anyway, regardless of what the fd=0A= represents. So I really do not understand what your worry is here. If you a= re=0A= worried about overhead/performance, then please show numbers. If something = is=0A= wrong, we can work on fixing it.=0A= =0A= > And if new features (zone-append for now) are available only on=0A= > ZoneFS, it forces application to use something that maynot be most=0A= > optimal for its need.=0A= =0A= "may" is not enough to convince me...=0A= =0A= > Coming to the original problem of plumbing append - I think divergence=0A= > started because RWF_APPEND did not have any meaning for block device.=0A= > Did I miss any other reason?=0A= =0A= Correct.=0A= =0A= > How about write-anywhere semantics (RWF_RELAXED_WRITE or=0A= > RWF_ANONYMOUS_WRITE flag) on block-dev.=0A= =0A= "write-anywhere" ? What do you mean ? That is not possible on zoned devices= ,=0A= even with zone append, since you at least need to guarantee that zones have= =0A= enough unwritten space to accept an append command.=0A= =0A= > Zone-append works a lot like write-anywhere on block-dev (or on any=0A= > other file that combines multiple-zones, in non-sequential fashion).=0A= =0A= That is an over-simplification that is not helpful at all. Zone append is n= ot=0A= "write anywhere" at all. And "write anywhere" is not a concept that exist o= n=0A= regular block devices anyway. Writes only go to the offset that the user=0A= decided, through lseek(), pwrite() or aio->aio_offset. It is not like the b= lock=0A= layer decides where the writes land. The same constraint applies to zone ap= pend:=0A= the user decide the target zone. That is not "anywhere". Please be precise = with=0A= wording and implied/desired semantic. Narrow down the scope of your concept= =0A= names for clarity.=0A= =0A= And talking about "file that combines multiple-zones" would mean that we ar= e now=0A= back in FS land, not raw block device file accesses anymore. So which one a= re we=0A= talking about ? It looks like you are confusing what the application does a= nd=0A= how it uses whatever usable interface to the device with what that interfac= e=0A= actually is. It is very confusing.=0A= =0A= >>> Also it seems difficult (compared to block dev) to fit simple-copy TP= =0A= >>> in ZoneFS. The new=0A= >>> command needs: one NVMe drive, list of source LBAs and one destination= =0A= >>> LBA. In ZoneFS, we would deal with N+1 file-descriptors (N source zone= =0A= >>> file, and one destination zone file) for that. While with block=0A= >>> interface, we do not need more than one file-descriptor representing= =0A= >>> the entire device. With more zone-files, we face open/close overhead to= o.=0A= >>=0A= >> Are you expecting simple-copy to allow requests that are not zone aligne= d ? I do=0A= >> not think that will ever happen. Otherwise, the gotcha cases for it woul= d be far=0A= >> too numerous. Simple-copy is essentially an optimized regular write comm= and.=0A= >> Similarly to that command, it will not allow copies over zone boundaries= and=0A= >> will need the destination LBA to be aligned to the destination zone WP. = I have=0A= >> not checked the TP though and given the NVMe NDA, I will stop the discus= sion here.=0A= > =0A= > TP is ratified, if that is the problem you are referring to.=0A= =0A= Ah. Yes. Got confused with ZRWA. Simple-copy is a different story anyway. L= et's=0A= not mix it into zone append user interface please.=0A= =0A= > =0A= >> filesend() could be used as the interface for simple-copy. Implementing = that in=0A= >> zonefs would not be that hard. What is your plan for simple-copy interfa= ce for=0A= >> raw block device ? An ioctl ? filesend() too ? As as with any other use= r level=0A= >> API, we should not be restricted to a particular device type if we can a= void it,=0A= >> so in-kernel emulation of the feature is needed for devices that do not = have=0A= >> simple-copy or scsi extended copy. filesend() seems to me like the best = choice=0A= >> since all of that is already implemented there.=0A= > =0A= > At this moment, ioctl as sync and io-uring for async. sendfile() and=0A= > copy_file_range() takes two fds....with that we can represent copy=0A= > from one source zone to another zone.=0A= > But it does not fit to represent larger copy (from N source zones to=0A= > one destination zone).=0A= =0A= nvme passthrough ? If that does not fit your use case, then think of an=0A= interface, its definition/semantic and propose it. But again, use a differe= nt=0A= thread. This is mixing up zone-append and simple copy, which I do not think= are=0A= directly related.=0A= =0A= > Not sure if I am clear, perhaps sending RFC would be better for=0A= > discussion on simple-copy.=0A= =0A= Separate this discussion from zone append please. Mixing up 2 problems in o= ne=0A= thread is not helpful to make progress.=0A= =0A= =0A= -- =0A= Damien Le Moal=0A= Western Digital Research=0A=