From: Mike Rapoport <rppt@xxxxxxxxxxxxx> Subject: 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@xxxxxxxxxx Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> Acked-by: Arnd Bergmann <arnd@xxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> Cc: Ivan Kokshaysky <ink@xxxxxxxxxxxxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Matt Turner <mattst88@xxxxxxxxx> Cc: Richard Henderson <rth@xxxxxxxxxxx> Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/admin-guide/sysctl/vm.rst | 12 ++--- Documentation/vm/memory-model.rst | 45 ---------------------- 2 files changed, 8 insertions(+), 49 deletions(-) --- a/Documentation/admin-guide/sysctl/vm.rst~docs-remove-description-of-discontigmem +++ a/Documentation/admin-guide/sysctl/vm.rst @@ -938,12 +938,12 @@ 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 --- a/Documentation/vm/memory-model.rst~docs-remove-description-of-discontigmem +++ a/Documentation/vm/memory-model.rst @@ -14,15 +14,11 @@ for the CPU. Then there could be several 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` 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 ========= _
