From: Dan Williams <dan.j.williams@intel.com>
To: akpm@linux-foundation.org
Cc: Jonathan Corbet <corbet@lwn.net>,
Mike Rapoport <rppt@linux.ibm.com>,
linux-mm@kvack.org, linux-nvdimm@lists.01.org,
linux-kernel@vger.kernel.org, osalvador@suse.de, mhocko@suse.com
Subject: [PATCH v9 09/12] mm: Document ZONE_DEVICE memory-model implications
Date: Wed, 05 Jun 2019 14:58:47 -0700 [thread overview]
Message-ID: <155977192794.2443951.16177998596403034849.stgit@dwillia2-desk3.amr.corp.intel.com> (raw)
In-Reply-To: <155977186863.2443951.9036044808311959913.stgit@dwillia2-desk3.amr.corp.intel.com>
Explain the general mechanisms of 'ZONE_DEVICE' pages and list the users
of 'devm_memremap_pages()'.
Cc: Jonathan Corbet <corbet@lwn.net>
Reported-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
Documentation/vm/memory-model.rst | 39 +++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)
diff --git a/Documentation/vm/memory-model.rst b/Documentation/vm/memory-model.rst
index 382f72ace1fc..e0af47e02e78 100644
--- a/Documentation/vm/memory-model.rst
+++ b/Documentation/vm/memory-model.rst
@@ -181,3 +181,42 @@ that is eventually passed to vmemmap_populate() through a long chain
of function calls. The vmemmap_populate() implementation may use the
`vmem_altmap` along with :c:func:`altmap_alloc_block_buf` helper to
allocate memory map on the persistent memory device.
+
+ZONE_DEVICE
+===========
+The `ZONE_DEVICE` facility builds upon `SPARSEMEM_VMEMMAP` to offer
+`struct page` `mem_map` services for device driver identified physical
+address ranges. The "device" aspect of `ZONE_DEVICE` relates to the fact
+that the page objects for these address ranges are never marked online,
+and that a reference must be taken against the device, not just the page
+to keep the memory pinned for active use. `ZONE_DEVICE`, via
+:c:func:`devm_memremap_pages`, performs just enough memory hotplug to
+turn on :c:func:`pfn_to_page`, :c:func:`page_to_pfn`, and
+:c:func:`get_user_pages` service for the given range of pfns. Since the
+page reference count never drops below 1 the page is never tracked as
+free memory and the page's `struct list_head lru` space is repurposed
+for back referencing to the host device / driver that mapped the memory.
+
+While `SPARSEMEM` presents memory as a collection of sections,
+optionally collected into memory blocks, `ZONE_DEVICE` users have a need
+for smaller granularity of populating the `mem_map`. Given that
+`ZONE_DEVICE` memory is never marked online it is subsequently never
+subject to its memory ranges being exposed through the sysfs memory
+hotplug api on memory block boundaries. The implementation relies on
+this lack of user-api constraint to allow sub-section sized memory
+ranges to be specified to :c:func:`arch_add_memory`, the top-half of
+memory hotplug. Sub-section support allows for `PMD_SIZE` as the minimum
+alignment granularity for :c:func:`devm_memremap_pages`.
+
+The users of `ZONE_DEVICE` are:
+* pmem: Map platform persistent memory to be used as a direct-I/O target
+ via DAX mappings.
+
+* hmm: Extend `ZONE_DEVICE` with `->page_fault()` and `->page_free()`
+ event callbacks to allow a device-driver to coordinate memory management
+ events related to device-memory, typically GPU memory. See
+ Documentation/vm/hmm.rst.
+
+* p2pdma: Create `struct page` objects to allow peer devices in a
+ PCI/-E topology to coordinate direct-DMA operations between themselves,
+ i.e. bypass host memory.
next prev parent reply other threads:[~2019-06-05 22:13 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-05 21:57 [PATCH v9 00/12] mm: Sub-section memory hotplug support Dan Williams
2019-06-05 21:57 ` [PATCH v9 01/12] mm/sparsemem: Introduce struct mem_section_usage Dan Williams
2019-06-06 17:34 ` Oscar Salvador
2019-06-16 13:11 ` Wei Yang
2019-06-18 21:56 ` Dan Williams
2019-06-19 2:13 ` Wei Yang
2019-06-05 21:57 ` [PATCH v9 02/12] mm/sparsemem: Add helpers track active portions of a section at boot Dan Williams
2019-06-06 16:55 ` Oscar Salvador
2019-06-17 22:21 ` Wei Yang
2019-06-17 22:32 ` Dan Williams
2019-06-18 1:03 ` Wei Yang
2019-06-19 3:15 ` Dan Williams
2019-06-05 21:58 ` [PATCH v9 03/12] mm/hotplug: Prepare shrink_{zone, pgdat}_span for sub-section removal Dan Williams
2019-06-18 1:42 ` Wei Yang
2019-06-19 3:40 ` Dan Williams
2019-06-05 21:58 ` [PATCH v9 04/12] mm/sparsemem: Convert kmalloc_section_memmap() to populate_section_memmap() Dan Williams
2019-06-06 17:02 ` Oscar Salvador
2019-06-16 6:06 ` Aneesh Kumar K.V
2019-06-05 21:58 ` [PATCH v9 05/12] mm/hotplug: Kill is_dev_zone() usage in __remove_pages() Dan Williams
2019-06-05 21:58 ` [PATCH v9 06/12] mm: Kill is_dev_zone() helper Dan Williams
2019-06-18 3:35 ` Wei Yang
2019-06-05 21:58 ` [PATCH v9 07/12] mm/sparsemem: Prepare for sub-section ranges Dan Williams
2019-06-06 17:21 ` Oscar Salvador
2019-06-06 18:16 ` Dan Williams
2019-06-14 8:39 ` David Hildenbrand
2019-06-05 21:58 ` [PATCH v9 08/12] mm/sparsemem: Support sub-section hotplug Dan Williams
2019-06-07 8:33 ` Oscar Salvador
2019-06-07 15:38 ` Dan Williams
2019-06-07 21:41 ` Oscar Salvador
2019-06-05 21:58 ` Dan Williams [this message]
2019-06-05 21:58 ` [PATCH v9 10/12] mm/devm_memremap_pages: Enable sub-section remap Dan Williams
2019-06-07 8:56 ` Oscar Salvador
2019-06-16 7:49 ` Aneesh Kumar K.V
2019-06-05 21:58 ` [PATCH v9 11/12] libnvdimm/pfn: Fix fsdax-mode namespace info-block zero-fields Dan Williams
2019-06-06 21:46 ` Andrew Morton
2019-06-06 22:06 ` Dan Williams
2019-06-07 19:54 ` Andrew Morton
2019-06-07 20:09 ` Dan Williams
2019-06-12 9:41 ` Aneesh Kumar K.V
2019-06-05 21:59 ` [PATCH v9 12/12] libnvdimm/pfn: Stop padding pmem namespaces to section alignment Dan Williams
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