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

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Message-ID: <x49lg07eb3d.fsf@segfault.boston.devel.redhat.com>
Date:   Thu, 18 Apr 2019 08:45:10 -0400
From:   Jeff Moyer <jmoyer@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Toshi Kani <toshi.kani@....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

Dan Williams <dan.j.williams@...el.com> writes:

>> 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.

Sure.  I'll also have a look over the patches.

-Jeff