4c21e2f244
Christoph Lameter demonstrated very poor scalability on the SGI 512-way, with a many-threaded application which concurrently initializes different parts of a large anonymous area. This patch corrects that, by using a separate spinlock per page table page, to guard the page table entries in that page, instead of using the mm's single page_table_lock. (But even then, page_table_lock is still used to guard page table allocation, and anon_vma allocation.) In this implementation, the spinlock is tucked inside the struct page of the page table page: with a BUILD_BUG_ON in case it overflows - which it would in the case of 32-bit PA-RISC with spinlock debugging enabled. Splitting the lock is not quite for free: another cacheline access. Ideally, I suppose we would use split ptlock only for multi-threaded processes on multi-cpu machines; but deciding that dynamically would have its own costs. So for now enable it by config, at some number of cpus - since the Kconfig language doesn't support inequalities, let preprocessor compare that with NR_CPUS. But I don't think it's worth being user-configurable: for good testing of both split and unsplit configs, split now at 4 cpus, and perhaps change that to 8 later. There is a benefit even for singly threaded processes: kswapd can be attacking one part of the mm while another part is busy faulting. Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
126 lines
4 KiB
Text
126 lines
4 KiB
Text
config SELECT_MEMORY_MODEL
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def_bool y
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depends on EXPERIMENTAL || ARCH_SELECT_MEMORY_MODEL
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choice
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prompt "Memory model"
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depends on SELECT_MEMORY_MODEL
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default DISCONTIGMEM_MANUAL if ARCH_DISCONTIGMEM_DEFAULT
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default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
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default FLATMEM_MANUAL
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config FLATMEM_MANUAL
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bool "Flat Memory"
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depends on !ARCH_DISCONTIGMEM_ENABLE || ARCH_FLATMEM_ENABLE
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help
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This option allows you to change some of the ways that
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Linux manages its memory internally. Most users will
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only have one option here: FLATMEM. This is normal
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and a correct option.
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Some users of more advanced features like NUMA and
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memory hotplug may have different options here.
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DISCONTIGMEM is an more mature, better tested system,
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but is incompatible with memory hotplug and may suffer
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decreased performance over SPARSEMEM. If unsure between
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"Sparse Memory" and "Discontiguous Memory", choose
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"Discontiguous Memory".
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If unsure, choose this option (Flat Memory) over any other.
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config DISCONTIGMEM_MANUAL
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bool "Discontiguous Memory"
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depends on ARCH_DISCONTIGMEM_ENABLE
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help
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This option provides enhanced support for discontiguous
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memory systems, over FLATMEM. These systems have holes
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in their physical address spaces, and this option provides
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more efficient handling of these holes. However, the vast
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majority of hardware has quite flat address spaces, and
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can have degraded performance from extra overhead that
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this option imposes.
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Many NUMA configurations will have this as the only option.
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If unsure, choose "Flat Memory" over this option.
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config SPARSEMEM_MANUAL
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bool "Sparse Memory"
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depends on ARCH_SPARSEMEM_ENABLE
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help
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This will be the only option for some systems, including
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memory hotplug systems. This is normal.
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For many other systems, this will be an alternative to
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"Discontiguous Memory". This option provides some potential
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performance benefits, along with decreased code complexity,
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but it is newer, and more experimental.
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If unsure, choose "Discontiguous Memory" or "Flat Memory"
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over this option.
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endchoice
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config DISCONTIGMEM
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def_bool y
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depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
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config SPARSEMEM
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def_bool y
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depends on SPARSEMEM_MANUAL
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config FLATMEM
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def_bool y
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depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
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config FLAT_NODE_MEM_MAP
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def_bool y
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depends on !SPARSEMEM
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#
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# Both the NUMA code and DISCONTIGMEM use arrays of pg_data_t's
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# to represent different areas of memory. This variable allows
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# those dependencies to exist individually.
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#
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config NEED_MULTIPLE_NODES
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def_bool y
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depends on DISCONTIGMEM || NUMA
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config HAVE_MEMORY_PRESENT
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def_bool y
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depends on ARCH_HAVE_MEMORY_PRESENT || SPARSEMEM
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#
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# SPARSEMEM_EXTREME (which is the default) does some bootmem
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# allocations when memory_present() is called. If this can not
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# be done on your architecture, select this option. However,
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# statically allocating the mem_section[] array can potentially
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# consume vast quantities of .bss, so be careful.
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#
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# This option will also potentially produce smaller runtime code
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# with gcc 3.4 and later.
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#
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config SPARSEMEM_STATIC
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def_bool n
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#
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# Architectecture platforms which require a two level mem_section in SPARSEMEM
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# must select this option. This is usually for architecture platforms with
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# an extremely sparse physical address space.
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#
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config SPARSEMEM_EXTREME
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def_bool y
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depends on SPARSEMEM && !SPARSEMEM_STATIC
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# Heavily threaded applications may benefit from splitting the mm-wide
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# page_table_lock, so that faults on different parts of the user address
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# space can be handled with less contention: split it at this NR_CPUS.
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# Default to 4 for wider testing, though 8 might be more appropriate.
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# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
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# PA-RISC's debug spinlock_t is too large for the 32-bit struct page.
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#
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config SPLIT_PTLOCK_CPUS
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int
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default "4096" if ARM && !CPU_CACHE_VIPT
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default "4096" if PARISC && DEBUG_SPINLOCK && !64BIT
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default "4"
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