Re: [PATCH v3 0/4] Devmap cleanups + arm64 support

From: Dan Williams <dan.j.williams@intel.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Michal Hocko <mhocko@suse.com>,
	"anshuman.khandual@arm.com" <anshuman.khandual@arm.com>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"will.deacon@arm.com" <will.deacon@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Christoph Hellwig <hch@infradead.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Robin Murphy <robin.murphy@arm.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v3 0/4] Devmap cleanups + arm64 support
Date: Thu, 4 Jul 2019 16:37:51 -0700	[thread overview]
Message-ID: <CAPcyv4iSviwyAPBnw5zDu_Ks0Ty0sFZ6QbEtVVU0PRd=ReRZNg@mail.gmail.com> (raw)
In-Reply-To: <20190704195934.GA23542@mellanox.com>

On Thu, Jul 4, 2019 at 12:59 PM Jason Gunthorpe <jgg@mellanox.com> wrote:
>
> On Thu, Jul 04, 2019 at 11:53:24AM -0700, Andrew Morton wrote:
> > On Wed, 26 Jun 2019 20:35:51 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > > > Let me know and I can help orchestate this.
> > >
> > > Well.  Whatever works.  In this situation I'd stage the patches after
> > > linux-next and would merge them up after the prereq patches have been
> > > merged into mainline.  Easy.
> >
> > All right, what the hell just happened?
>
> Christoph's patch series for the devmap & hmm rework finally made it
> into linux-next, sorry, it took quite a few iterations on the list to
> get all the reviews and tests, and figure out how to resolve some
> other conflicting things. So it just made it this week.
>
> Recall, this is the patch series I asked you about routing a few weeks
> ago, as it really exceeded the small area that hmm.git was supposed to
> cover. I think we are both caught off guard how big the conflict is!
>
> > A bunch of new material has just been introduced into linux-next.
> > I've partially unpicked the resulting mess, haven't dared trying to
> > compile it yet.  To get this far I'll need to drop two patch series
> > and one individual patch:
>
> > mm-clean-up-is_device__page-definitions.patch
> > mm-introduce-arch_has_pte_devmap.patch
> > arm64-mm-implement-pte_devmap-support.patch
> > arm64-mm-implement-pte_devmap-support-fix.patch
>
> This one we discussed, and I thought we agreed would go to your 'stage
> after linux-next' flow (see above). I think the conflict was minor
> here.
>
> > mm-sparsemem-introduce-struct-mem_section_usage.patch
> > mm-sparsemem-introduce-a-section_is_early-flag.patch
> > mm-sparsemem-add-helpers-track-active-portions-of-a-section-at-boot.patch
> > mm-hotplug-prepare-shrink_zone-pgdat_span-for-sub-section-removal.patch
> > mm-sparsemem-convert-kmalloc_section_memmap-to-populate_section_memmap.patch
> > mm-hotplug-kill-is_dev_zone-usage-in-__remove_pages.patch
> > mm-kill-is_dev_zone-helper.patch
> > mm-sparsemem-prepare-for-sub-section-ranges.patch
> > mm-sparsemem-support-sub-section-hotplug.patch
> > mm-document-zone_device-memory-model-implications.patch
> > mm-document-zone_device-memory-model-implications-fix.patch
> > mm-devm_memremap_pages-enable-sub-section-remap.patch
> > libnvdimm-pfn-fix-fsdax-mode-namespace-info-block-zero-fields.patch
> > libnvdimm-pfn-stop-padding-pmem-namespaces-to-section-alignment.patch
>
> Dan pointed to this while reviewing CH's series and said the conflicts
> would be manageable, but they are certainly larger than I expected!
>
> This series is the one that seems to be the really big trouble. I
> already checked all the other stuff that Stephen resolved, and it
> looks OK and managable. Just this one conflict with kernel/memremap.c
> is beyond me.
>
> What approach do you want to take to go forward? Here are some thoughts:
>
> CH has said he is away for the long weekend, so the path that involves
> the fewest people is if Dan respins the above on linux-next and it
> goes later with the arm patches above, assuming defering it for now
> has no other adverse effects on -mm.
>
> Pushing CH's series to -mm would need a respin on top of Dan's series
> above and would need to carry along the whole hmm.git (about 44
> patches). Signs are that this could be managed with the code currently
> in the GPU trees.
>
> If we give up on CH's series the hmm.git will not have conflicts,
> however we just kick the can to the next merge window where we will be
> back to having to co-ordinate amd/nouveau/rdma git trees and -mm's
> patch workflow - and I think we will be worse off as we will have
> totally given up on a git based work flow for this. :(

I think the problem would be resolved going forward post-v5.3 since we
won't have two tress managing kernel/memremap.c. This cycle however
there is a backlog of kernel/memremap.c changes in -mm.

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