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Petersen" , Kanchan Joshi , "hare@suse.de" , "sagi@grimberg.me" , "brauner@kernel.org" , "viro@zeniv.linux.org.uk" , "jack@suse.cz" , "jaegeuk@kernel.org" , "bcrl@kvack.org" , "dhowells@redhat.com" , "bvanassche@acm.org" , "asml.silence@gmail.com" , "linux-nvme@lists.infradead.org" , "linux-fsdevel@vger.kernel.org" , "io-uring@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-aio@kvack.org" , "gost.dev@samsung.com" , "vishak.g@samsung.com" Subject: RE: [PATCH v7 0/3] FDP and per-io hints Thread-Topic: [PATCH v7 0/3] FDP and per-io hints Thread-Index: AQHbG7xJFahlOOmkRUWBz3B/P2gFpLKBuCIAgAQCOYCAABtsUP///IcAgAAiAcA= Date: Mon, 14 Oct 2024 09:08:24 +0000 Message-ID: <9e3792eebf7f427db7c466374972fb99@CAMSVWEXC02.scsc.local> In-Reply-To: <20241014074708.GA22575@lst.de> Accept-Language: en-US, en-GB Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFupgk+LIzCtJLcpLzFFi42LZduzned2u+zzpBp++SFvMWbWN0WL13X42 i65/W1gsXh/+xGgx7cNPZot3Tb9ZLPYsmsRksXL1USaLd63nWCxmT29msniyfhazxaRD1xgt pkxrYrTYe0vbYs/ekywW85c9ZbdYfvwfk8W61+9ZLM7/Pc7qIOxx+Yq3x85Zd9k9zt/byOJx +Wypx6ZVnWwemz5NYvfYvKTeY/fNBjaPj09vsXi833eVzePMgiNA8dPVHp83yXlsevKWKYAv issmJTUnsyy1SN8ugStj4dKPLAUPVCp2rPnG3sC4SLaLkZNDQsBE4sfDJcxdjFwcQgIrGCXe TZnGBuF8YZSY/+YiVOYzo8S8NwtYYFqWnnnCCJFYDlR1ZwoLXNXiSb1QmTOMEgtWnYHqX8ko 8elrFxtIP5uAvsSq7acYQWwRASWJp6/OgnUwC1xjlzjYc4YJJCEsYCDRvGQfVJGhxLtlC6Fs P4mf336BHcIioCrxZu4UdhCbV8BVouXMN7A4p4COxLIFJ8HmMArISjxa+QushllAXOLWk/lM EE8ISiyavYcZwhaT+LfrIRuEbSCxdek+qEcVJfrmv2eB6NWRWLD7ExuErS2xbOFrZoi9ghIn Zz4B+19C4CSXxJf5j9ghml0kZv67DmULS7w6vgXKlpE4PbkHakG1RMPJE0wTGLVmIblvFpJ9 s5Dsm4Vk3wJGllWM4qmlxbnpqcXGeanlesWJucWleel6yfm5mxiBifX0v+NfdzCuePVR7xAj EwfjIUYJDmYlEd73UznThXhTEiurUovy44tKc1KLDzFKc7AoifOqpsinCgmkJ5akZqemFqQW wWSZODilGphqQ1Q+LPbgq+m7KHbI4Vv3+YR17W6Mp6z3rhQJPP7Haf+kk5rHHsYtkQpdoJiQ PlP48VbzqmX6666tbXpZ0P/kYfujDdE7Ugtmhv/co/KJudt3q/PZuhet5e9Zbe63vIzW1frM fcbW23DNHolDe6ayMMpdFZTRnKvRxz8l80+597aecuVlUmXRB90V+RwOsx0/Lp57VqJedu9L NrWr6fqbfTbN1+GXvCPJUXjZnvtrTw5vbmCX0M1tfSovNs1+xDj3s4bD1a7fafaHecrn77ao kf92c1XVgyVLT6woe72hTonf6J5v0oXHifF8844lHVCsNRM8pcrW+3T6X4Ui9h6O1HCjnAL7 S3w3dl09kaXEUpyRaKjFXFScCACFqAVQGwQAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFvrOKsWRmVeSWpSXmKPExsVy+t/xu7qd93nSDR5Os7GYs2obo8Xqu/1s Fl3/trBYvD78idFi2oefzBbvmn6zWOxZNInJYuXqo0wW71rPsVjMnt7MZPFk/Sxmi0mHrjFa TJnWxGix95a2xZ69J1ks5i97ym6x/Pg/Jot1r9+zWJz/e5zVQdjj8hVvj52z7rJ7nL+3kcXj 8tlSj02rOtk8Nn2axO6xeUm9x+6bDWweH5/eYvF4v+8qm8eZBUeA4qerPT5vkvPY9OQtUwBf lJ5NUX5pSapCRn5xia1StKGFkZ6hpYWekYmlnqGxeayVkamSvp1NSmpOZllqkb5dgl7GwqUf WQoeqFTsWPONvYFxkWwXIyeHhICJxNIzTxi7GLk4hASWMkr8+drCBJGQkdj45SorhC0s8eda FxtE0UdGidPHLzKCJIQEzjBKbL0TApFYySix+McDNpAEm4C+xKrtp8CKRASUJJ6+Ogu2glng CrtE86LnYAlhAQOJ5iX7oIoMJd4tWwhl+0n8/PaLBcRmEVCVeDN3CjuIzSvgKtFy5hsLxLZf zBIb1lwGa+AU0JFYtuAk2N2MArISj1b+AmtgFhCXuPVkPtQ/AhJL9pxnhrBFJV4+/gf1m4HE 1qX7WCBsRYm++e9ZIHp1JBbs/sQGYWtLLFv4mhniCEGJkzOfsExglJqFZMUsJC2zkLTMQtKy gJFlFaNIamlxbnpusZFecWJucWleul5yfu4mRmAK3Hbs55YdjCtffdQ7xMjEwXiIUYKDWUmE 9/1UznQh3pTEyqrUovz4otKc1OJDjKbAgJnILCWanA9Mwnkl8YZmBqaGJmaWBqaWZsZK4rxs V86nCQmkJ5akZqemFqQWwfQxcXBKNTD5HcjP5Z8t3Ten+GZ9vAWD98qcjtdRaYGJJttEDxx9 cvL0lfnMhe4Bv4JCG4sK46wOXuaaHtqisUp3w0vBKof5Ze28K9LmH2T70CbaN1PYq7tLvHZn xtXsp1Fx1dv8ZcWdlV5eWtIo9ma9/aRPzhmtKuvDuJ9NOThb72J1x/a7Ow0D0v98X/0gxd2o c/+PYtuHC1j3RRRMT96b/9rjyW7HHUKnlniGumuz3vp2PimpI3/25ORq6QfNB+SOLJvVt2qD jmPJn8ZIP4PksnMcMdtvGjr8UfnPsrb5cLPUWTch7VZuNhlTf/WJ4fWs2foSYosu80pIztn+ RXLTrdmXchet7V7qo5LJ/kBp907d9UosxRmJhlrMRcWJAMKylzUKBAAA X-CMS-MailID: 20241014090826eucas1p20a1b983ba65066f2970d11ae6e5518c5 X-Msg-Generator: CA X-RootMTR: 20241010070738eucas1p2057209e5f669f37ca586ad4a619289ed X-EPHeader: CA CMS-TYPE: 201P X-CMS-RootMailID: 20241010070738eucas1p2057209e5f669f37ca586ad4a619289ed References: <20241009092828.GA18118@lst.de> <20241010070736.de32zgad4qmfohhe@ArmHalley.local> <20241010091333.GB9287@lst.de> <20241010115914.eokdnq2cmcvwoeis@ArmHalley.local> <20241011090224.GC4039@lst.de> <5e9f7f1c-48fd-477f-b4ba-c94e6b50b56f@kernel.dk> <20241014062125.GA21033@lst.de> <34d3ad68068f4f87bf0a61ea8fb8f217@CAMSVWEXC02.scsc.local> <20241014074708.GA22575@lst.de> > -----Original Message----- > From: Christoph Hellwig > Sent: Monday, October 14, 2024 9:47 AM > To: Javier Gonzalez > Cc: Christoph Hellwig ; Jens Axboe ; Keith B= usch > ; Martin K. Petersen ; Kan= chan > Joshi ; hare@suse.de; sagi@grimberg.me; > brauner@kernel.org; viro@zeniv.linux.org.uk; jack@suse.cz; jaegeuk@kernel= .org; > bcrl@kvack.org; dhowells@redhat.com; bvanassche@acm.org; > asml.silence@gmail.com; linux-nvme@lists.infradead.org; linux- > fsdevel@vger.kernel.org; io-uring@vger.kernel.org; linux-block@vger.kerne= l.org; > linux-aio@kvack.org; gost.dev@samsung.com; vishak.g@samsung.com > Subject: Re: [PATCH v7 0/3] FDP and per-io hints >=20 > On Mon, Oct 14, 2024 at 07:02:11AM +0000, Javier Gonzalez wrote: > > > And exactly that is the problem. For file systems we can't support > > > that sanely. So IFF you absolutely want the per-I/O hints we need > > > an opt in by the file operations. I've said that at least twice > > > in this discussion before, but as everyone likes to have political > > > discussions instead of technical ones no one replied to that. > > > > Is it a way forward to add this in a new spin of the series - keeping t= he > > temperature mapping on the NVMe side? >=20 > What do you gain from that? NVMe does not understand data temperatures, > so why make up that claim? =20 I expressed this a couple of times in this thread. It is no problem to map = temperatures to a protocol that does not understand the semantics. It is not perfect, an= d in time I agree that we would benefit from exposing the raw hints without semantics= from Block layer upwards. But the temperatures are already there. We are not adding anything new. And= thanks to this, we can enable existing users with _minimal_ changes to user-space.= As pointed on the XFS zoned discussions, this is very similar to what you guys are doi= ng (exactly to re-use what it is already there), and it works. On top of this, applicatio= ns that already understand temperatures (e.g., RocksDB) will be able to leverage FDP SSDs w= ithout changes. > Especially as it directly undermindes any file system work to actually ma= ke use of it. I do not think it does. If a FS wants to use the temperatures, then they wo= uld be able to leverage FDP besides SCSI. And if we come up with a better interface later on, we ca= n make the changes then. I really do not see the issue. If we were adding a temperature abstraction = now, I would agree with You that we would need to cover the use-case you mention for FSs from the b= eginning, but this Is already here. Seems like a fair compromise to support current users. >=20 > > If not, what would be acceptable for a first version, before getting in= to adding > > a new interface to expose agnostic hints? >=20 > Just iterate on Kanchan's series for a block layer (and possible user lev= el, > but that's less urgent) interface for stream separation? We can work on this later, but it is not that easy. Look at the mail I forw= arded=20 Form Christian. We now can store hints in the same structure as the tempera= tures.=20 I believe that we would be able to support 128 hints. If we are serious abo= ut supporting=20 hints as a general interface, 128 hints is not nearly enough. Moreover: - How do we convince VFS folks to give us more space for hints at this po= int? - How do we make agnostic hints and temperature co-exist? Do we use a bit= to select=20 and create a protocol? This seems over-complicated - When we are exposing general hints to the block layer, how do we suppor= t N:N=20 FS:Block_Devices? and DMs? This is not obvious, and it goes well beyon= d what we need today, but we probably need to think about it. =20 And these are just questions that we know. You see that this is a big lift = (which we=20 can work together on!), but will delay current users by months. And honestl= y, I do not feel comfortable doing this alone; we need application and FS folks li= ke you to=20 help guide this so that it is really usable. I say it again: Your idea about properly supporting hints in FS is good, an= d I think we should work on it. But I do not believe that the current patches (with added thing= s like opt in file ops)=20 get in the way of this. So if the disagreement is if these patches are har= mful, let's talk about=20 this explicitly and try to agree; we do not need to go over the need for a = new hint interface.=20 We already agree on this.