linux-kernel - Re: [PATCH v6 01/12] mm/sparsemem: Introduce struct mem_section

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Message-ID: <CA+CK2bA_5uaEK1vjOwNZC9Ta+T-_yTL9etOUEvOUSrtNEOe8og@mail.gmail.com>
Date:   Thu, 2 May 2019 10:16:08 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Logan Gunthorpe <logang@...tatee.com>,
        Linux MM <linux-mm@...ck.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v6 01/12] mm/sparsemem: Introduce struct mem_section_usage

On Thu, May 2, 2019 at 2:07 AM Dan Williams <dan.j.williams@...el.com> wrote:
>
> On Wed, May 1, 2019 at 4:25 PM Pavel Tatashin <pasha.tatashin@...een.com> wrote:
> >
> > On 19-04-17 11:39:00, Dan Williams wrote:
> > > Towards enabling memory hotplug to track partial population of a
> > > section, introduce 'struct mem_section_usage'.
> > >
> > > A pointer to a 'struct mem_section_usage' instance replaces the existing
> > > pointer to a 'pageblock_flags' bitmap. Effectively it adds one more
> > > 'unsigned long' beyond the 'pageblock_flags' (usemap) allocation to
> > > house a new 'map_active' bitmap.  The new bitmap enables the memory
> > > hot{plug,remove} implementation to act on incremental sub-divisions of a
> > > section.
> > >
> > > The primary motivation for this functionality is to support platforms
> > > that mix "System RAM" and "Persistent Memory" within a single section,
> > > or multiple PMEM ranges with different mapping lifetimes within a single
> > > section. The section restriction for hotplug has caused an ongoing saga
> > > of hacks and bugs for devm_memremap_pages() users.
> > >
> > > Beyond the fixups to teach existing paths how to retrieve the 'usemap'
> > > from a section, and updates to usemap allocation path, there are no
> > > expected behavior changes.
> > >
> > > Cc: Michal Hocko <mhocko@...e.com>
> > > Cc: Vlastimil Babka <vbabka@...e.cz>
> > > Cc: Logan Gunthorpe <logang@...tatee.com>
> > > Signed-off-by: Dan Williams <dan.j.williams@...el.com>

Reviewed-by: Pavel Tatashin <pasha.tatashin@...een.com>