Based on kernel version 2.6.26. Page generated on 2008-07-16 21:13 EST.
1 Started Nov 1999 by Kanoj Sarcar <kanoj[AT]sgi[DOT]com> 2 3 The intent of this file is to have an uptodate, running commentary 4 from different people about NUMA specific code in the Linux vm. 5 6 What is NUMA? It is an architecture where the memory access times 7 for different regions of memory from a given processor varies 8 according to the "distance" of the memory region from the processor. 9 Each region of memory to which access times are the same from any 10 cpu, is called a node. On such architectures, it is beneficial if 11 the kernel tries to minimize inter node communications. Schemes 12 for this range from kernel text and read-only data replication 13 across nodes, and trying to house all the data structures that 14 key components of the kernel need on memory on that node. 15 16 Currently, all the numa support is to provide efficient handling 17 of widely discontiguous physical memory, so architectures which 18 are not NUMA but can have huge holes in the physical address space 19 can use the same code. All this code is bracketed by CONFIG_DISCONTIGMEM. 20 21 The initial port includes NUMAizing the bootmem allocator code by 22 encapsulating all the pieces of information into a bootmem_data_t 23 structure. Node specific calls have been added to the allocator. 24 In theory, any platform which uses the bootmem allocator should 25 be able to put the bootmem and mem_map data structures anywhere 26 it deems best. 27 28 Each node's page allocation data structures have also been encapsulated 29 into a pg_data_t. The bootmem_data_t is just one part of this. To 30 make the code look uniform between NUMA and regular UMA platforms, 31 UMA platforms have a statically allocated pg_data_t too (contig_page_data). 32 For the sake of uniformity, the function num_online_nodes() is also defined 33 for all platforms. As we run benchmarks, we might decide to NUMAize 34 more variables like low_on_memory, nr_free_pages etc into the pg_data_t. 35 36 The NUMA aware page allocation code currently tries to allocate pages 37 from different nodes in a round robin manner. This will be changed to 38 do concentratic circle search, starting from current node, once the 39 NUMA port achieves more maturity. The call alloc_pages_node has been 40 added, so that drivers can make the call and not worry about whether 41 it is running on a NUMA or UMA platform.