From: Baoquan He <bhe@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, richardw.yang@linux.intel.com,
david@redhat.com, osalvador@suse.de, dan.j.williams@intel.com,
rppt@linux.ibm.com, robin.murphy@arm.com
Subject: Re: [PATCH v2 0/7] mm/hotplug: Only use subsection map in VMEMMAP case
Date: Wed, 26 Feb 2020 11:44:33 +0800 [thread overview]
Message-ID: <20200226034433.GE24216@MiWiFi-R3L-srv> (raw)
In-Reply-To: <20200225100352.GN22443@dhcp22.suse.cz>
On 02/25/20 at 11:03am, Michal Hocko wrote:
> On Fri 21-02-20 22:28:47, Baoquan He wrote:
> > On 02/20/20 at 11:38am, Michal Hocko wrote:
> > > On Thu 20-02-20 12:33:09, Baoquan He wrote:
> > > > Memory sub-section hotplug was added to fix the issue that nvdimm could
> > > > be mapped at non-section aligned starting address. A subsection map is
> > > > added into struct mem_section_usage to implement it. However, sub-section
> > > > is only supported in VMEMMAP case.
> > >
> > > Why? Is there any fundamental reason or just a lack of implementation?
> > > VMEMMAP should be really only an implementation detail unless I am
> > > missing something subtle.
> >
> > Thanks for checking.
> >
> > VMEMMAP is one of two ways to convert a PFN to the corresponding
> > 'struct page' in SPARSE model. I mentioned them as VMEMMAP case, or
> > !VMEMMAP case because we called them like this previously when reviewed
> > patches, hope it won't cause confusion.
> >
> > Currently, config ZONE_DEVICE depends on SPARSEMEM_VMEMMAP. The
> > subsection_map is added to struct mem_section_usage to track which sub
> > section is present, VMEMMAP fills those bits which corresponding
> > sub-sections are present, while !VMEMMAP, namely classic SPARSE, fills
> > the whole map always.
> >
> > As we know, VMEMMAP builds page table to map a cluster of 'struct page'
> > into the corresponding area of 'vmemmap'. Subsection hotplug can be
> > supported naturally, w/o any change, just map needed region related to
> > sub-sections on demand. For !VMEMMAP, it allocates memmap with
> > alloc_pages() or vmalloc, thing is a little complicated, e.g the mixed
> > section, boot memory occupies the starting area, later pmem hot added to
> > the rear part.
> >
> > About !VMEMMAP which doesn't support sub-section hotplog, Dan said
> > it's more because the effort and maintenance burden outweighs the
> > benefit. And the current 64 bit ARCHes all enable
> > SPARSEMEM_VMEMMAP_ENABLE by default.
>
> OK, if this is the primary argument then make sure to document it in the
> changelog (cover letter).
Will add it when repost.
prev parent reply other threads:[~2020-02-26 3:44 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 4:33 Baoquan He
2020-02-20 4:33 ` [PATCH v2 1/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case Baoquan He
2020-02-20 6:11 ` Wei Yang
2020-02-20 12:07 ` David Hildenbrand
2020-02-26 12:31 ` David Hildenbrand
2020-02-26 13:07 ` Baoquan He
2020-02-26 18:09 ` Dan Williams
2020-03-03 8:34 ` David Hildenbrand
2020-03-03 8:39 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 2/7] mm/sparse.c: introduce new function fill_subsection_map() Baoquan He
2020-02-20 6:14 ` Wei Yang
2020-02-28 14:27 ` David Hildenbrand
2020-03-01 4:59 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 3/7] mm/sparse.c: introduce a new function clear_subsection_map() Baoquan He
2020-02-20 6:15 ` Wei Yang
2020-02-28 14:36 ` David Hildenbrand
2020-03-01 5:20 ` Baoquan He
2020-03-02 15:43 ` David Hildenbrand
2020-03-03 1:53 ` Baoquan He
2020-03-03 8:22 ` Baoquan He
2020-03-03 8:33 ` David Hildenbrand
2020-03-03 8:38 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 4/7] mm/sparse.c: only use subsection map in VMEMMAP case Baoquan He
2020-02-20 6:17 ` Wei Yang
2020-02-25 9:57 ` Michal Hocko
2020-02-26 3:53 ` Baoquan He
2020-02-26 9:10 ` Michal Hocko
2020-02-28 7:25 ` Baoquan He
2020-02-20 4:33 ` [PATCH v2 5/7] mm/sparse.c: add code comment about sub-section hotplug Baoquan He
2020-02-20 4:33 ` [PATCH v2 6/7] mm/sparse.c: move subsection_map related codes together Baoquan He
2020-02-20 6:18 ` Wei Yang
2020-02-20 7:04 ` Baoquan He
2020-02-20 7:12 ` Wei Yang
2020-02-20 8:55 ` Baoquan He
2020-02-20 21:52 ` Wei Yang
2020-02-20 4:33 ` [PATCH v2 7/7] mm/sparse.c: Use __get_free_pages() instead in populate_section_memmap() Baoquan He
2020-02-20 10:38 ` [PATCH v2 0/7] mm/hotplug: Only use subsection map in VMEMMAP case Michal Hocko
2020-02-21 14:28 ` Baoquan He
2020-02-25 9:10 ` David Hildenbrand
2020-02-25 10:02 ` Michal Hocko
2020-02-26 3:42 ` Baoquan He
2020-02-26 9:14 ` Michal Hocko
2020-02-26 12:30 ` Baoquan He
2020-02-25 10:03 ` Michal Hocko
2020-02-26 3:44 ` Baoquan He [this message]
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