Root/mm/Kconfig

1config SELECT_MEMORY_MODEL
2    def_bool y
3    depends on EXPERIMENTAL || ARCH_SELECT_MEMORY_MODEL
4
5choice
6    prompt "Memory model"
7    depends on SELECT_MEMORY_MODEL
8    default DISCONTIGMEM_MANUAL if ARCH_DISCONTIGMEM_DEFAULT
9    default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
10    default FLATMEM_MANUAL
11
12config FLATMEM_MANUAL
13    bool "Flat Memory"
14    depends on !(ARCH_DISCONTIGMEM_ENABLE || ARCH_SPARSEMEM_ENABLE) || ARCH_FLATMEM_ENABLE
15    help
16      This option allows you to change some of the ways that
17      Linux manages its memory internally. Most users will
18      only have one option here: FLATMEM. This is normal
19      and a correct option.
20
21      Some users of more advanced features like NUMA and
22      memory hotplug may have different options here.
23      DISCONTIGMEM is an more mature, better tested system,
24      but is incompatible with memory hotplug and may suffer
25      decreased performance over SPARSEMEM. If unsure between
26      "Sparse Memory" and "Discontiguous Memory", choose
27      "Discontiguous Memory".
28
29      If unsure, choose this option (Flat Memory) over any other.
30
31config DISCONTIGMEM_MANUAL
32    bool "Discontiguous Memory"
33    depends on ARCH_DISCONTIGMEM_ENABLE
34    help
35      This option provides enhanced support for discontiguous
36      memory systems, over FLATMEM. These systems have holes
37      in their physical address spaces, and this option provides
38      more efficient handling of these holes. However, the vast
39      majority of hardware has quite flat address spaces, and
40      can have degraded performance from the extra overhead that
41      this option imposes.
42
43      Many NUMA configurations will have this as the only option.
44
45      If unsure, choose "Flat Memory" over this option.
46
47config SPARSEMEM_MANUAL
48    bool "Sparse Memory"
49    depends on ARCH_SPARSEMEM_ENABLE
50    help
51      This will be the only option for some systems, including
52      memory hotplug systems. This is normal.
53
54      For many other systems, this will be an alternative to
55      "Discontiguous Memory". This option provides some potential
56      performance benefits, along with decreased code complexity,
57      but it is newer, and more experimental.
58
59      If unsure, choose "Discontiguous Memory" or "Flat Memory"
60      over this option.
61
62endchoice
63
64config DISCONTIGMEM
65    def_bool y
66    depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
67
68config SPARSEMEM
69    def_bool y
70    depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
71
72config FLATMEM
73    def_bool y
74    depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
75
76config FLAT_NODE_MEM_MAP
77    def_bool y
78    depends on !SPARSEMEM
79
80#
81# Both the NUMA code and DISCONTIGMEM use arrays of pg_data_t's
82# to represent different areas of memory. This variable allows
83# those dependencies to exist individually.
84#
85config NEED_MULTIPLE_NODES
86    def_bool y
87    depends on DISCONTIGMEM || NUMA
88
89config HAVE_MEMORY_PRESENT
90    def_bool y
91    depends on ARCH_HAVE_MEMORY_PRESENT || SPARSEMEM
92
93#
94# SPARSEMEM_EXTREME (which is the default) does some bootmem
95# allocations when memory_present() is called. If this cannot
96# be done on your architecture, select this option. However,
97# statically allocating the mem_section[] array can potentially
98# consume vast quantities of .bss, so be careful.
99#
100# This option will also potentially produce smaller runtime code
101# with gcc 3.4 and later.
102#
103config SPARSEMEM_STATIC
104    bool
105
106#
107# Architecture platforms which require a two level mem_section in SPARSEMEM
108# must select this option. This is usually for architecture platforms with
109# an extremely sparse physical address space.
110#
111config SPARSEMEM_EXTREME
112    def_bool y
113    depends on SPARSEMEM && !SPARSEMEM_STATIC
114
115config SPARSEMEM_VMEMMAP_ENABLE
116    bool
117
118config SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
119    def_bool y
120    depends on SPARSEMEM && X86_64
121
122config SPARSEMEM_VMEMMAP
123    bool "Sparse Memory virtual memmap"
124    depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
125    default y
126    help
127     SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
128     pfn_to_page and page_to_pfn operations. This is the most
129     efficient option when sufficient kernel resources are available.
130
131config HAVE_MEMBLOCK
132    boolean
133
134# eventually, we can have this option just 'select SPARSEMEM'
135config MEMORY_HOTPLUG
136    bool "Allow for memory hot-add"
137    depends on SPARSEMEM || X86_64_ACPI_NUMA
138    depends on HOTPLUG && ARCH_ENABLE_MEMORY_HOTPLUG
139    depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
140
141config MEMORY_HOTPLUG_SPARSE
142    def_bool y
143    depends on SPARSEMEM && MEMORY_HOTPLUG
144
145config MEMORY_HOTREMOVE
146    bool "Allow for memory hot remove"
147    depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
148    depends on MIGRATION
149
150#
151# If we have space for more page flags then we can enable additional
152# optimizations and functionality.
153#
154# Regular Sparsemem takes page flag bits for the sectionid if it does not
155# use a virtual memmap. Disable extended page flags for 32 bit platforms
156# that require the use of a sectionid in the page flags.
157#
158config PAGEFLAGS_EXTENDED
159    def_bool y
160    depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
161
162# Heavily threaded applications may benefit from splitting the mm-wide
163# page_table_lock, so that faults on different parts of the user address
164# space can be handled with less contention: split it at this NR_CPUS.
165# Default to 4 for wider testing, though 8 might be more appropriate.
166# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
167# PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
168# DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
169#
170config SPLIT_PTLOCK_CPUS
171    int
172    default "999999" if ARM && !CPU_CACHE_VIPT
173    default "999999" if PARISC && !PA20
174    default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC
175    default "4"
176
177#
178# support for memory compaction
179config COMPACTION
180    bool "Allow for memory compaction"
181    select MIGRATION
182    depends on EXPERIMENTAL && HUGETLB_PAGE && MMU
183    help
184      Allows the compaction of memory for the allocation of huge pages.
185
186#
187# support for page migration
188#
189config MIGRATION
190    bool "Page migration"
191    def_bool y
192    depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION
193    help
194      Allows the migration of the physical location of pages of processes
195      while the virtual addresses are not changed. This is useful in
196      two situations. The first is on NUMA systems to put pages nearer
197      to the processors accessing. The second is when allocating huge
198      pages as migration can relocate pages to satisfy a huge page
199      allocation instead of reclaiming.
200
201config PHYS_ADDR_T_64BIT
202    def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
203
204config ZONE_DMA_FLAG
205    int
206    default "0" if !ZONE_DMA
207    default "1"
208
209config BOUNCE
210    def_bool y
211    depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
212
213config NR_QUICK
214    int
215    depends on QUICKLIST
216    default "2" if AVR32
217    default "1"
218
219config VIRT_TO_BUS
220    def_bool y
221    depends on !ARCH_NO_VIRT_TO_BUS
222
223config MMU_NOTIFIER
224    bool
225
226config KSM
227    bool "Enable KSM for page merging"
228    depends on MMU
229    help
230      Enable Kernel Samepage Merging: KSM periodically scans those areas
231      of an application's address space that an app has advised may be
232      mergeable. When it finds pages of identical content, it replaces
233      the many instances by a single page with that content, so
234      saving memory until one or another app needs to modify the content.
235      Recommended for use with KVM, or with other duplicative applications.
236      See Documentation/vm/ksm.txt for more information: KSM is inactive
237      until a program has madvised that an area is MADV_MERGEABLE, and
238      root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
239
240config DEFAULT_MMAP_MIN_ADDR
241        int "Low address space to protect from user allocation"
242    depends on MMU
243        default 4096
244        help
245      This is the portion of low virtual memory which should be protected
246      from userspace allocation. Keeping a user from writing to low pages
247      can help reduce the impact of kernel NULL pointer bugs.
248
249      For most ia64, ppc64 and x86 users with lots of address space
250      a value of 65536 is reasonable and should cause no problems.
251      On arm and other archs it should not be higher than 32768.
252      Programs which use vm86 functionality or have some need to map
253      this low address space will need CAP_SYS_RAWIO or disable this
254      protection by setting the value to 0.
255
256      This value can be changed after boot using the
257      /proc/sys/vm/mmap_min_addr tunable.
258
259config ARCH_SUPPORTS_MEMORY_FAILURE
260    bool
261
262config MEMORY_FAILURE
263    depends on MMU
264    depends on ARCH_SUPPORTS_MEMORY_FAILURE
265    bool "Enable recovery from hardware memory errors"
266    help
267      Enables code to recover from some memory failures on systems
268      with MCA recovery. This allows a system to continue running
269      even when some of its memory has uncorrected errors. This requires
270      special hardware support and typically ECC memory.
271
272config HWPOISON_INJECT
273    tristate "HWPoison pages injector"
274    depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
275    select PROC_PAGE_MONITOR
276
277config NOMMU_INITIAL_TRIM_EXCESS
278    int "Turn on mmap() excess space trimming before booting"
279    depends on !MMU
280    default 1
281    help
282      The NOMMU mmap() frequently needs to allocate large contiguous chunks
283      of memory on which to store mappings, but it can only ask the system
284      allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
285      more than it requires. To deal with this, mmap() is able to trim off
286      the excess and return it to the allocator.
287
288      If trimming is enabled, the excess is trimmed off and returned to the
289      system allocator, which can cause extra fragmentation, particularly
290      if there are a lot of transient processes.
291
292      If trimming is disabled, the excess is kept, but not used, which for
293      long-term mappings means that the space is wasted.
294
295      Trimming can be dynamically controlled through a sysctl option
296      (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
297      excess pages there must be before trimming should occur, or zero if
298      no trimming is to occur.
299
300      This option specifies the initial value of this option. The default
301      of 1 says that all excess pages should be trimmed.
302
303      See Documentation/nommu-mmap.txt for more information.
304

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