linux-kernel - Re: [PATCH v6 00/12] mm: Sub-section memory hotplug support

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Message-ID: <CAPcyv4iW=xhhUQbg0bt=xCgVaR_jUvATeLxSoCfvzG5gTEAX6A@mail.gmail.com>
Date:   Wed, 17 Apr 2019 19:09:12 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Toshi Kani <toshi.kani@....com>,
        Jeff Moyer <jmoyer@...hat.com>, Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        stable <stable@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        osalvador@...e.de
Subject: Re: [PATCH v6 00/12] mm: Sub-section memory hotplug support

On Wed, Apr 17, 2019 at 3:59 PM Dan Williams <dan.j.williams@...el.com> wrote:
>
> On Wed, Apr 17, 2019 at 3:04 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > On Wed, 17 Apr 2019 11:38:55 -0700 Dan Williams <dan.j.williams@...el.com> wrote:
> >
> > > The memory hotplug section is an arbitrary / convenient unit for memory
> > > hotplug. 'Section-size' units have bled into the user interface
> > > ('memblock' sysfs) and can not be changed without breaking existing
> > > userspace. The section-size constraint, while mostly benign for typical
> > > memory hotplug, has and continues to wreak havoc with 'device-memory'
> > > use cases, persistent memory (pmem) in particular. Recall that pmem uses
> > > devm_memremap_pages(), and subsequently arch_add_memory(), to allocate a
> > > 'struct page' memmap for pmem. However, it does not use the 'bottom
> > > half' of memory hotplug, i.e. never marks pmem pages online and never
> > > exposes the userspace memblock interface for pmem. This leaves an
> > > opening to redress the section-size constraint.
> >
> > v6 and we're not showing any review activity.  Who would be suitable
> > people to help out here?
>
> There was quite a bit of review of the cover letter from Michal and
> David, but you're right the details not so much as of yet. I'd like to
> call out other people where I can reciprocate with some review of my
> own. Oscar's altmap work looks like a good candidate for that.

I'm also hoping Jeff can give a tested-by for the customer scenarios
that fall over with the current implementation.