Messages in this thread | | | Subject | Re: multipath-tools: add ANA support for NVMe device | From | Hannes Reinecke <> | Date | Wed, 14 Nov 2018 08:49:23 +0100 |
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On 11/14/18 6:38 AM, Mike Snitzer wrote: > On Tue, Nov 13 2018 at 1:00pm -0500, > Mike Snitzer <snitzer@redhat.com> wrote: > >> On Tue, Nov 13 2018 at 11:18am -0500, >> Keith Busch <keith.busch@intel.com> wrote: >> >>> On Mon, Nov 12, 2018 at 04:53:23PM -0500, Mike Snitzer wrote: >>>> On Mon, Nov 12 2018 at 11:23am -0500, >>>> Martin Wilck <mwilck@suse.com> wrote: >>>> >>>>> Hello Lijie, >>>>> >>>>> On Thu, 2018-11-08 at 14:09 +0800, lijie wrote: >>>>>> Add support for Asynchronous Namespace Access as specified in NVMe >>>>>> 1.3 >>>>>> TP 4004. The states are updated through reading the ANA log page. >>>>>> >>>>>> By default, the native nvme multipath takes over the nvme device. >>>>>> We can pass a false to the parameter 'multipath' of the nvme-core.ko >>>>>> module,when we want to use multipath-tools. >>>>> >>>>> Thank you for the patch. It looks quite good to me. I've tested it with >>>>> a Linux target and found no problems so far. >>>>> >>>>> I have a few questions and comments inline below. >>>>> >>>>> I suggest you also have a look at detect_prio(); it seems to make sense >>>>> to use the ana prioritizer for NVMe paths automatically if ANA is >>>>> supported (with your patch, "detect_prio no" and "prio ana" have to be >>>>> configured explicitly). But that can be done in a later patch. >>>> >>>> I (and others) think it makes sense to at least triple check with the >>>> NVMe developers (now cc'd) to see if we could get agreement on the nvme >>>> driver providing the ANA state via sysfs (when modparam >>>> nvme_core.multipath=N is set), like Hannes proposed here: >>>> http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html >>>> >>>> Then the userspace multipath-tools ANA support could just read sysfs >>>> rather than reinvent harvesting the ANA state via ioctl. >>> >>> I'd prefer not duplicating the log page parsing. Maybe nvme's shouldn't >>> even be tied to CONFIG_NVME_MULTIPATH so that the 'multipath' param >>> isn't even an issue. >> >> I like your instincts, we just need to take them a bit further. >> >> Splitting out the kernel's ANA log page parsing won't buy us much given >> it is userspace (multipath-tools) that needs to consume it. The less >> work userspace needs to do (because kernel has already done it) the >> better. >> >> If the NVMe driver is made to always track and export the ANA state via >> sysfs [1] we'd avoid userspace parsing duplication "for free". This >> should occur regardless of what layer is reacting to the ANA state >> changes (be it NVMe's native multipathing or multipath-tools). >> >> ANA and NVMe multipathing really are disjoint, making them tightly >> coupled only serves to force NVMe driver provided multipathing _or_ >> userspace ANA state tracking duplication that really isn't ideal [2]. >> >> We need a reasoned answer to the primary question of whether the NVMe >> maintainers are willing to cooperate by providing this basic ANA sysfs >> export even if nvme_core.multipath=N [1]. >> >> Christoph said "No" [3], but offered little _real_ justification for why >> this isn't the right thing for NVMe in general. > ... >> [1]: http://lists.infradead.org/pipermail/linux-nvme/2018-November/020765.html >> [2]: https://www.redhat.com/archives/dm-devel/2018-November/msg00072.html > ... > > I knew there had to be a pretty tight coupling between the NVMe driver's > native multipathing and ANA support... and that the simplicity of > Hannes' patch [1] was too good to be true. > > The real justification for not making Hannes' change is it'd effectively > be useless without first splitting out the ANA handling done during NVMe > request completion (NVME_SC_ANA_* cases in nvme_failover_req) that > triggers re-reading the ANA log page accordingly. > > So without the ability to drive the ANA workqueue to trigger > nvme_read_ana_log() from the nvme driver's completion path -- even if > nvme_core.multipath=N -- it really doesn't buy multipath-tools anything > to have the NVMe driver export the ana state via sysfs, because that ANA > state will never get updated. > Hmm. Indeed, I was more focussed on having the sysfs attributes displayed, so yes, indeed it needs some more work.
>> The inability to provide proper justification for rejecting a patch >> (that already had one co-maintainer's Reviewed-by [5]) _should_ render >> that rejection baseless, and the patch applied (especially if there is >> contributing subsystem developer interest in maintaining this support >> over time, which there is). At least that is what would happen in a >> properly maintained kernel subsystem. >> >> It'd really go a long way if senior Linux NVMe maintainers took steps to >> accept reasonable changes. > > Even though I'm frustrated I was clearly too harsh and regret my tone. > I promise to _try_ to suck less. > > This dynamic of terse responses or no responses at all whenever NVMe > driver changes to ease multipath-tools NVMe support are floated is the > depressing gift that keeps on giving. But enough excuses... > > Not holding my breath BUT: > if decoupling the reading of ANA state from native NVMe multipathing > specific work during nvme request completion were an acceptable > advancement I'd gladly do the work. > I'd be happy to work on that, given that we'll have to have 'real' ANA support for device-mapper anyway for SLE12 SP4 etc.
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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