Re: [PATCH 2/4] ndctl/namespace: Check for seed namespaces earlier

From: Oliver <oohall@gmail.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>
Subject: Re: [PATCH 2/4] ndctl/namespace: Check for seed namespaces earlier
Date: Tue, 8 Jan 2019 22:00:21 +1100	[thread overview]
Message-ID: <CAOSf1CF=z--oNjvYW1KZCzcFQOgbMqvooqWqt7=1bqZK3UFcGw@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4hCds_vziivz164p5-zZcsB7kHV68imE3orw87y9A8TKA@mail.gmail.com>

On Tue, Jan 8, 2019 at 1:59 PM Dan Williams <dan.j.williams@intel.com> wrote:
>
> Sorry for letting this conversation go cold, lets try to revive it as
> Vishal is looking to cut an ndctl v64 in the coming days and it would
> be good to include this support.
>
> On Tue, Nov 27, 2018 at 5:27 AM Oliver <oohall@gmail.com> wrote:
> >
> > On Mon, Nov 26, 2018 at 7:12 AM Dan Williams <dan.j.williams@intel.com> wrote:
> > >
> > > On Mon, Nov 19, 2018 at 12:11 AM Oliver O'Halloran <oohall@gmail.com> wrote:
> > > >
> > > > When creating an fsdax or devdax namespace we need to verify that the
> > > > seed namespaces exist. This patch reworks the validation so that it's
> > > > done earlier to simplify the subsequent patches in the series.
> > > >
> > > > No functional changes.
> > >
> > > It does appear to have a functional change. do_setup_pfn() supports
> > > the case of statically allocated namespaces in NDCTL_NS_MODE_MEMORY
> > > mode.
> >
> > Hmm, ok. Up until now I had assumed that as far as ndctl was concerned
> > NS_MODE_MEMORY was synonymous with a pfn namespace.
> >
> > > This is what one gets by default with "legacy" pmem defined as
> > > E820-type-12 memory. In that case the kernel assumes that the
> > > resulting memmap is always small enough to be allocated from DRAM and
> > > there is no need to use a dynamic  pfn device. So, if I'm not
> > > mistaken, the deletion of do_setup_pfn() loses that special case
> > > handling.
> >
> > From what I see, the main difference is that ndctl would fail
> > validation when fsdax mode is specified and there's no pfn namespace
> > support in the kernel. I agree that's not great, but I'm not sure what
> > we should be doing here. The current behaviour will silently ignore -a
> > if "-m fsdax -M mem" is specified in the reconfigure case, which
> > doesn't seem great either.
>
> Right, both issues need to be addressed. As far as I can see
> do_setup_pfn() just needs to be extended to detect attempts to set a
> non-default alignment, and then when setting the alignment require it
> to be one of the supported values.

Seems reasonable. I'll dust off the series and post a respin tomorrow.

> I expect we should also extend the region listing output to include
> the supported alignments.

Probably a good idea. I think even have a patch to do that somewhere...

> Does this clarify your concern enough to attempt a respin of the
> series? If not just holler and Vishal and I will arm-wrestle to decide
> who picks this up.
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