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

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Message-ID: <20190620170027.GA7126@linux>
Date:   Thu, 20 Jun 2019 19:00:35 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     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>,
        Jeff Moyer <jmoyer@...hat.com>, Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>, stable@...r.kernel.org,
        Wei Yang <richardw.yang@...ux.intel.com>, linux-mm@...ck.org,
        linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 00/13] mm: Sub-section memory hotplug support

On Tue, Jun 18, 2019 at 10:51:33PM -0700, Dan Williams wrote:
> 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/

Hi Dan,

I am planning to give it a final review later tomorrow.
Now that this work is settled, I took the chance to dust off and push my
vmemmap-hotplug, and I am working on that right now.
But I would definetely come back to this tomorrow.

Thanks for the work

-- 
Oscar Salvador
SUSE L3