Subject: [PATCH v2 7/9] docs: remove description of DISCONTIGMEM

From: Mike Rapoport <[email-masked]>
Date: Fri, 4 Jun 2021 09:49:14 +0300

From: Mike Rapoport <[email-masked]>

Remove description of DISCONTIGMEM from the "Memory Models" document and
update VM sysctl description so that it won't mention DISCONIGMEM.

Signed-off-by: Mike Rapoport <[email-masked]>
---
 Documentation/admin-guide/sysctl/vm.rst | 12 +++----
 Documentation/vm/memory-model.rst       | 45 ++-----------------------
 2 files changed, 8 insertions(+), 49 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index 586cd4b86428..ddbd71d592e0 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -936,12 +936,12 @@ allocations, THP and hugetlbfs pages.
 
 To make it sensible with respect to the watermark_scale_factor
 parameter, the unit is in fractions of 10,000. The default value of
-15,000 on !DISCONTIGMEM configurations means that up to 150% of the high
-watermark will be reclaimed in the event of a pageblock being mixed due
-to fragmentation. The level of reclaim is determined by the number of
-fragmentation events that occurred in the recent past. If this value is
-smaller than a pageblock then a pageblocks worth of pages will be reclaimed
-(e.g.  2MB on 64-bit x86). A boost factor of 0 will disable the feature.
+15,000 means that up to 150% of the high watermark will be reclaimed in the
+event of a pageblock being mixed due to fragmentation. The level of reclaim
+is determined by the number of fragmentation events that occurred in the
+recent past. If this value is smaller than a pageblock then a pageblocks
+worth of pages will be reclaimed (e.g.  2MB on 64-bit x86). A boost factor
+of 0 will disable the feature.

 watermark_scale_factor
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
 =========
 
-- 
2.28.0