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authorLinus Torvalds <torvalds@linux-foundation.org>2019-07-19 19:45:58 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2019-07-19 19:45:58 +0300
commit249be8511b269495bc95cb8bdfdd5840b2ba73c0 (patch)
tree6920bde053faa0284b52b2a9c9695f5516520377 /Documentation
parent3bfe1fc46794631366faa3ef075e1b0ff7ba120a (diff)
parenteec4844fae7c033a0c1fc1eb3b8517aeb8b6cc49 (diff)
downloadlinux-249be8511b269495bc95cb8bdfdd5840b2ba73c0.tar.xz
Merge branch 'akpm' (patches from Andrew)
Merge yet more updates from Andrew Morton: "The rest of MM and a kernel-wide procfs cleanup. Summary of the more significant patches: - Patch series "mm/memory_hotplug: Factor out memory block devicehandling", v3. David Hildenbrand. Some spring-cleaning of the memory hotplug code, notably in drivers/base/memory.c - "mm: thp: fix false negative of shmem vma's THP eligibility". Yang Shi. Fix /proc/pid/smaps output for THP pages used in shmem. - "resource: fix locking in find_next_iomem_res()" + 1. Nadav Amit. Bugfix and speedup for kernel/resource.c - Patch series "mm: Further memory block device cleanups", David Hildenbrand. More spring-cleaning of the memory hotplug code. - Patch series "mm: Sub-section memory hotplug support". Dan Williams. Generalise the memory hotplug code so that pmem can use it more completely. Then remove the hacks from the libnvdimm code which were there to work around the memory-hotplug code's constraints. - "proc/sysctl: add shared variables for range check", Matteo Croce. We have about 250 instances of int zero; ... .extra1 = &zero, in the tree. This is a tree-wide sweep to make all those private "zero"s and "one"s use global variables. Alas, it isn't practical to make those two global integers const" * emailed patches from Andrew Morton <akpm@linux-foundation.org>: (38 commits) proc/sysctl: add shared variables for range check mm: migrate: remove unused mode argument mm/sparsemem: cleanup 'section number' data types libnvdimm/pfn: stop padding pmem namespaces to section alignment libnvdimm/pfn: fix fsdax-mode namespace info-block zero-fields mm/devm_memremap_pages: enable sub-section remap mm: document ZONE_DEVICE memory-model implications mm/sparsemem: support sub-section hotplug mm/sparsemem: prepare for sub-section ranges mm: kill is_dev_zone() helper mm/hotplug: kill is_dev_zone() usage in __remove_pages() mm/sparsemem: convert kmalloc_section_memmap() to populate_section_memmap() mm/hotplug: prepare shrink_{zone, pgdat}_span for sub-section removal mm/sparsemem: add helpers track active portions of a section at boot mm/sparsemem: introduce a SECTION_IS_EARLY flag mm/sparsemem: introduce struct mem_section_usage drivers/base/memory.c: get rid of find_memory_block_hinted() mm/memory_hotplug: move and simplify walk_memory_blocks() mm/memory_hotplug: rename walk_memory_range() and pass start+size instead of pfns mm: make register_mem_sect_under_node() static ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/proc.txt4
-rw-r--r--Documentation/vm/memory-model.rst40
2 files changed, 42 insertions, 2 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index fb4735fd73b0..99ca040e3f90 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -486,8 +486,8 @@ replaced by copy-on-write) part of the underlying shmem object out on swap.
"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
does not take into account swapped out page of underlying shmem objects.
"Locked" indicates whether the mapping is locked in memory or not.
-"THPeligible" indicates whether the mapping is eligible for THP pages - 1 if
-true, 0 otherwise.
+"THPeligible" indicates whether the mapping is eligible for allocating THP
+pages - 1 if true, 0 otherwise. It just shows the current status.
"VmFlags" field deserves a separate description. This member represents the kernel
flags associated with the particular virtual memory area in two letter encoded
diff --git a/Documentation/vm/memory-model.rst b/Documentation/vm/memory-model.rst
index 382f72ace1fc..58a12376b7df 100644
--- a/Documentation/vm/memory-model.rst
+++ b/Documentation/vm/memory-model.rst
@@ -181,3 +181,43 @@ 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 2MB as the cross-arch
+common 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.