42 lines
2.2 KiB
Text
42 lines
2.2 KiB
Text
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Started Nov 1999 by Kanoj Sarcar <kanoj@sgi.com>
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The intent of this file is to have an uptodate, running commentary
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from different people about NUMA specific code in the Linux vm.
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What is NUMA? It is an architecture where the memory access times
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for different regions of memory from a given processor varies
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according to the "distance" of the memory region from the processor.
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Each region of memory to which access times are the same from any
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cpu, is called a node. On such architectures, it is beneficial if
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the kernel tries to minimize inter node communications. Schemes
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for this range from kernel text and read-only data replication
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across nodes, and trying to house all the data structures that
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key components of the kernel need on memory on that node.
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Currently, all the numa support is to provide efficient handling
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of widely discontiguous physical memory, so architectures which
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are not NUMA but can have huge holes in the physical address space
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can use the same code. All this code is bracketed by CONFIG_DISCONTIGMEM.
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The initial port includes NUMAizing the bootmem allocator code by
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encapsulating all the pieces of information into a bootmem_data_t
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structure. Node specific calls have been added to the allocator.
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In theory, any platform which uses the bootmem allocator should
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be able to to put the bootmem and mem_map data structures anywhere
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it deems best.
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Each node's page allocation data structures have also been encapsulated
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into a pg_data_t. The bootmem_data_t is just one part of this. To
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make the code look uniform between NUMA and regular UMA platforms,
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UMA platforms have a statically allocated pg_data_t too (contig_page_data).
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For the sake of uniformity, the function num_online_nodes() is also defined
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for all platforms. As we run benchmarks, we might decide to NUMAize
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more variables like low_on_memory, nr_free_pages etc into the pg_data_t.
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The NUMA aware page allocation code currently tries to allocate pages
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from different nodes in a round robin manner. This will be changed to
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do concentratic circle search, starting from current node, once the
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NUMA port achieves more maturity. The call alloc_pages_node has been
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added, so that drivers can make the call and not worry about whether
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it is running on a NUMA or UMA platform.
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