linux-kernel - Re: [PATCH v10 00/13] mm: Sub-section memory hotplug support

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Message-ID: <CAPcyv4ioWRhU9AbyTHhf9PavL0GSs=6h3dGyaQPb7vLJ2+z23g@mail.gmail.com>
Date:   Thu, 20 Jun 2019 09:30:10 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Jane Chu <jane.chu@...cle.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Jonathan Corbet <corbet@....net>, Qian Cai <cai@....pw>,
        Logan Gunthorpe <logang@...tatee.com>,
        Toshi Kani <toshi.kani@....com>,
        Oscar Salvador <osalvador@...e.de>,
        Jeff Moyer <jmoyer@...hat.com>, Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        stable <stable@...r.kernel.org>,
        Wei Yang <richardw.yang@...ux.intel.com>,
        Linux MM <linux-mm@...ck.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10 00/13] mm: Sub-section memory hotplug support

On Thu, Jun 20, 2019 at 5:31 AM Aneesh Kumar K.V
<aneesh.kumar@...ux.ibm.com> wrote:
>
> Dan Williams <dan.j.williams@...el.com> writes:
>
> > Changes since v9 [1]:
> > - Fix multiple issues related to the fact that pfn_valid() has
> >   traditionally returned true for any pfn in an 'early' (onlined at
> >   boot) section regardless of whether that pfn represented 'System RAM'.
> >   Teach pfn_valid() to maintain its traditional behavior in the presence
> >   of subsections. Specifically, subsection precision for pfn_valid() is
> >   only considered for non-early / hot-plugged sections. (Qian)
> >
> > - Related to the first item introduce a SECTION_IS_EARLY
> >   (->section_mem_map flag) to remove the existing hacks for determining
> >   an early section by looking at whether the usemap was allocated from the
> >   slab.
> >
> > - Kill off the EEXIST hackery in __add_pages(). It breaks
> >   (arch_add_memory() false-positive) the detection of subsection
> >   collisions reported by section_activate(). It is also obviated by
> >   David's recent reworks to move the 'System RAM' request_region() earlier
> >   in the add_memory() sequence().
> >
> > - Switch to an arch-independent / static subsection-size of 2MB.
> >   Otherwise, a per-arch subsection-size is a roadblock on the path to
> >   persistent memory namespace compatibility across archs. (Jeff)
> >
> > - Update the changelog for "libnvdimm/pfn: Fix fsdax-mode namespace
> >   info-block zero-fields" to clarify that the "Cc: stable" is only there
> >   as safety measure for a distro that decides to backport "libnvdimm/pfn:
> >   Stop padding pmem namespaces to section alignment", otherwise there is
> >   no known bug exposure in older kernels. (Andrew)
> >
> > - Drop some redundant subsection checks (Oscar)
> >
> > - Collect some reviewed-bys
> >
> > [1]: https://lore.kernel.org/lkml/155977186863.2443951.9036044808311959913.stgit@dwillia2-desk3.amr.corp.intel.com/
>
>
> You can add Tested-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> for ppc64.

Thank you!

> BTW even after this series we have the kernel crash mentioned in the
> below email on reconfigure.
>
> https://lore.kernel.org/linux-mm/20190514025354.9108-1-aneesh.kumar@linux.ibm.com
>
> I guess we need to conclude how the reserve space struct page should be
> initialized ?

Yes, that issue is independent of the subsection changes. I'll take a
closer look.