From: osalvador@suse.de
To: Dan Williams <dan.j.williams@intel.com>
Cc: akpm@linux-foundation.org, Michal Hocko <mhocko@suse.com>,
Vlastimil Babka <vbabka@suse.cz>,
Logan Gunthorpe <logang@deltatee.com>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
linux-nvdimm@lists.01.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, owner-linux-mm@kvack.org
Subject: Re: [PATCH v8 01/12] mm/sparsemem: Introduce struct mem_section_usage
Date: Fri, 10 May 2019 15:30:29 +0200 [thread overview]
Message-ID: <dd7b53bd986d79a94ac0b08e32336e44@suse.de> (raw)
In-Reply-To: <155718597192.130019.7128788290111464258.stgit@dwillia2-desk3.amr.corp.intel.com>
On 2019-05-07 01:39, 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 'subsection_map' bitmap. The new bitmap enables the memory
> hot{plug,remove} implementation to act on incremental sub-divisions of
> a
> section.
>
> The default SUBSECTION_SHIFT is chosen to keep the 'subsection_map' no
> larger than a single 'unsigned long' on the major architectures.
> Alternatively an architecture can define ARCH_SUBSECTION_SHIFT to
> override the default PMD_SHIFT. Note that PowerPC needs to use
> ARCH_SUBSECTION_SHIFT to workaround PMD_SHIFT being a non-constant
> expression on PowerPC.
>
> 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@suse.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> arch/powerpc/include/asm/sparsemem.h | 3 +
> include/linux/mmzone.h | 48 +++++++++++++++++++-
> mm/memory_hotplug.c | 18 ++++----
> mm/page_alloc.c | 2 -
> mm/sparse.c | 81
> +++++++++++++++++-----------------
> 5 files changed, 99 insertions(+), 53 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/sparsemem.h
> b/arch/powerpc/include/asm/sparsemem.h
> index 3192d454a733..1aa3c9303bf8 100644
> --- a/arch/powerpc/include/asm/sparsemem.h
> +++ b/arch/powerpc/include/asm/sparsemem.h
> @@ -10,6 +10,9 @@
> */
> #define SECTION_SIZE_BITS 24
>
> +/* Reflect the largest possible PMD-size as the subsection-size
> constant */
> +#define ARCH_SUBSECTION_SHIFT 24
> +
I guess this is done because PMD_SHIFT is defined at runtime rather at
compile time,
right?
> #endif /* CONFIG_SPARSEMEM */
>
> #ifdef CONFIG_MEMORY_HOTPLUG
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 70394cabaf4e..ef8d878079f9 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1160,6 +1160,44 @@ static inline unsigned long
> section_nr_to_pfn(unsigned long sec)
> #define SECTION_ALIGN_UP(pfn) (((pfn) + PAGES_PER_SECTION - 1) &
> PAGE_SECTION_MASK)
> #define SECTION_ALIGN_DOWN(pfn) ((pfn) & PAGE_SECTION_MASK)
>
> +/*
> + * SUBSECTION_SHIFT must be constant since it is used to declare
> + * subsection_map and related bitmaps without triggering the
> generation
> + * of variable-length arrays. The most natural size for a subsection
> is
> + * a PMD-page. For architectures that do not have a constant PMD-size
> + * ARCH_SUBSECTION_SHIFT can be set to a constant max size, or
> otherwise
> + * fallback to 2MB.
> + */
> +#if defined(ARCH_SUBSECTION_SHIFT)
> +#define SUBSECTION_SHIFT (ARCH_SUBSECTION_SHIFT)
> +#elif defined(PMD_SHIFT)
> +#define SUBSECTION_SHIFT (PMD_SHIFT)
> +#else
> +/*
> + * Memory hotplug enabled platforms avoid this default because they
> + * either define ARCH_SUBSECTION_SHIFT, or PMD_SHIFT is a constant,
> but
> + * this is kept as a backstop to allow compilation on
> + * !ARCH_ENABLE_MEMORY_HOTPLUG archs.
> + */
> +#define SUBSECTION_SHIFT 21
> +#endif
> +
> +#define PFN_SUBSECTION_SHIFT (SUBSECTION_SHIFT - PAGE_SHIFT)
> +#define PAGES_PER_SUBSECTION (1UL << PFN_SUBSECTION_SHIFT)
> +#define PAGE_SUBSECTION_MASK ((~(PAGES_PER_SUBSECTION-1)))
> +
> +#if SUBSECTION_SHIFT > SECTION_SIZE_BITS
> +#error Subsection size exceeds section size
> +#else
> +#define SUBSECTIONS_PER_SECTION (1UL << (SECTION_SIZE_BITS -
> SUBSECTION_SHIFT))
> +#endif
On powerpc, SUBSECTIONS_PER_SECTION will equal 1 (so one big section),
is that to be expected?
Will subsection_map_init handle this right?
next prev parent reply other threads:[~2019-05-10 13:30 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-06 23:39 [PATCH v8 00/12] mm: Sub-section memory hotplug support Dan Williams
2019-05-06 23:39 ` [PATCH v8 01/12] mm/sparsemem: Introduce struct mem_section_usage Dan Williams
2019-05-10 13:30 ` osalvador [this message]
2019-05-10 19:38 ` Dan Williams
2019-05-06 23:39 ` [PATCH v8 02/12] mm/memremap: Rename and consolidate SECTION_SIZE Dan Williams
2019-05-06 23:39 ` [PATCH v8 03/12] mm/sparsemem: Add helpers track active portions of a section at boot Dan Williams
2019-05-10 12:56 ` osalvador
2019-05-06 23:39 ` [PATCH v8 04/12] mm/hotplug: Prepare shrink_{zone, pgdat}_span for sub-section removal Dan Williams
2019-05-06 23:39 ` [PATCH v8 05/12] mm/sparsemem: Convert kmalloc_section_memmap() to populate_section_memmap() Dan Williams
2019-05-06 23:39 ` [PATCH v8 06/12] mm/hotplug: Kill is_dev_zone() usage in __remove_pages() Dan Williams
2019-05-06 23:40 ` [PATCH v8 07/12] mm: Kill is_dev_zone() helper Dan Williams
2019-05-06 23:40 ` [PATCH v8 08/12] mm/sparsemem: Prepare for sub-section ranges Dan Williams
2019-05-10 13:00 ` osalvador
2019-05-06 23:40 ` [PATCH v8 09/12] mm/sparsemem: Support sub-section hotplug Dan Williams
2019-05-08 23:15 ` Oscar Salvador
2019-05-13 13:54 ` Oscar Salvador
2019-06-04 4:47 ` Dan Williams
2019-05-06 23:40 ` [PATCH v8 10/12] mm/devm_memremap_pages: Enable sub-section remap Dan Williams
2019-05-06 23:40 ` [PATCH v8 11/12] libnvdimm/pfn: Fix fsdax-mode namespace info-block zero-fields Dan Williams
2019-05-06 23:40 ` [PATCH v8 12/12] libnvdimm/pfn: Stop padding pmem namespaces to section alignment Dan Williams
2019-05-13 21:01 ` [PATCH v8 00/12] mm: Sub-section memory hotplug support Mike Rapoport
2019-05-13 21:11 ` Dan Williams
2019-06-04 7:41 ` Oscar Salvador
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