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authorMike Rapoport <rppt@linux.ibm.com>2021-06-29 05:42:58 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-06-29 20:53:55 +0300
commit48d9f3355a8eaa79b00472929b517df497fc6d5f (patch)
tree2a6807a86ebccf7daca13eba09685cb1bf6621ea /Documentation/vm
parentd3c251ab95b69f3dc189c4657baeac1b4c050789 (diff)
downloadlinux-48d9f3355a8eaa79b00472929b517df497fc6d5f.tar.xz
docs: remove description of DISCONTIGMEM
Remove description of DISCONTIGMEM from the "Memory Models" document and update VM sysctl description so that it won't mention DISCONIGMEM. Link: https://lkml.kernel.org/r/20210608091316.3622-8-rppt@kernel.org Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Acked-by: Arnd Bergmann <arnd@arndb.de> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Matt Turner <mattst88@gmail.com> Cc: Richard Henderson <rth@twiddle.net> Cc: Vineet Gupta <vgupta@synopsys.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/vm')
-rw-r--r--Documentation/vm/memory-model.rst45
1 files changed, 2 insertions, 43 deletions
diff --git a/Documentation/vm/memory-model.rst b/Documentation/vm/memory-model.rst
index ce398a7dc6cd..30e8fbed6914 100644
--- a/Documentation/vm/memory-model.rst
+++ b/Documentation/vm/memory-model.rst
@@ -14,15 +14,11 @@ for the CPU. Then there could be several contiguous ranges at
completely distinct addresses. And, don't forget about NUMA, where
different memory banks are attached to different CPUs.
-Linux abstracts this diversity using one of the three memory models:
-FLATMEM, DISCONTIGMEM and SPARSEMEM. Each architecture defines what
+Linux abstracts this diversity using one of the two memory models:
+FLATMEM and SPARSEMEM. Each architecture defines what
memory models it supports, what the default memory model is and
whether it is possible to manually override that default.
-.. note::
- At time of this writing, DISCONTIGMEM is considered deprecated,
- although it is still in use by several architectures.
-
All the memory models track the status of physical page frames using
struct page arranged in one or more arrays.
@@ -63,43 +59,6 @@ straightforward: `PFN - ARCH_PFN_OFFSET` is an index to the
The `ARCH_PFN_OFFSET` defines the first page frame number for
systems with physical memory starting at address different from 0.
-DISCONTIGMEM
-============
-
-The DISCONTIGMEM model treats the physical memory as a collection of
-`nodes` similarly to how Linux NUMA support does. For each node Linux
-constructs an independent memory management subsystem represented by
-`struct pglist_data` (or `pg_data_t` for short). Among other
-things, `pg_data_t` holds the `node_mem_map` array that maps
-physical pages belonging to that node. The `node_start_pfn` field of
-`pg_data_t` is the number of the first page frame belonging to that
-node.
-
-The architecture setup code should call :c:func:`free_area_init_node` for
-each node in the system to initialize the `pg_data_t` object and its
-`node_mem_map`.
-
-Every `node_mem_map` behaves exactly as FLATMEM's `mem_map` -
-every physical page frame in a node has a `struct page` entry in the
-`node_mem_map` array. When DISCONTIGMEM is enabled, a portion of the
-`flags` field of the `struct page` encodes the node number of the
-node hosting that page.
-
-The conversion between a PFN and the `struct page` in the
-DISCONTIGMEM model became slightly more complex as it has to determine
-which node hosts the physical page and which `pg_data_t` object
-holds the `struct page`.
-
-Architectures that support DISCONTIGMEM provide :c:func:`pfn_to_nid`
-to convert PFN to the node number. The opposite conversion helper
-:c:func:`page_to_nid` is generic as it uses the node number encoded in
-page->flags.
-
-Once the node number is known, the PFN can be used to index
-appropriate `node_mem_map` array to access the `struct page` and
-the offset of the `struct page` from the `node_mem_map` plus
-`node_start_pfn` is the PFN of that page.
-
SPARSEMEM
=========