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
134config HAVE_MEMBLOCK_NODE_MAP
135    boolean
136
137config ARCH_DISCARD_MEMBLOCK
138    boolean
139
140config NO_BOOTMEM
141    boolean
142
143config MEMORY_ISOLATION
144    boolean
145
146# eventually, we can have this option just 'select SPARSEMEM'
147config MEMORY_HOTPLUG
148    bool "Allow for memory hot-add"
149    select MEMORY_ISOLATION
150    depends on SPARSEMEM || X86_64_ACPI_NUMA
151    depends on HOTPLUG && ARCH_ENABLE_MEMORY_HOTPLUG
152    depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
153
154config MEMORY_HOTPLUG_SPARSE
155    def_bool y
156    depends on SPARSEMEM && MEMORY_HOTPLUG
157
158config MEMORY_HOTREMOVE
159    bool "Allow for memory hot remove"
160    depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
161    depends on MIGRATION
162
163#
164# If we have space for more page flags then we can enable additional
165# optimizations and functionality.
166#
167# Regular Sparsemem takes page flag bits for the sectionid if it does not
168# use a virtual memmap. Disable extended page flags for 32 bit platforms
169# that require the use of a sectionid in the page flags.
170#
171config PAGEFLAGS_EXTENDED
172    def_bool y
173    depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
174
175# Heavily threaded applications may benefit from splitting the mm-wide
176# page_table_lock, so that faults on different parts of the user address
177# space can be handled with less contention: split it at this NR_CPUS.
178# Default to 4 for wider testing, though 8 might be more appropriate.
179# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
180# PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
181# DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
182#
183config SPLIT_PTLOCK_CPUS
184    int
185    default "999999" if ARM && !CPU_CACHE_VIPT
186    default "999999" if PARISC && !PA20
187    default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC
188    default "4"
189
190#
191# support for memory compaction
192config COMPACTION
193    bool "Allow for memory compaction"
194    select MIGRATION
195    depends on MMU
196    help
197      Allows the compaction of memory for the allocation of huge pages.
198
199#
200# support for page migration
201#
202config MIGRATION
203    bool "Page migration"
204    def_bool y
205    depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA
206    help
207      Allows the migration of the physical location of pages of processes
208      while the virtual addresses are not changed. This is useful in
209      two situations. The first is on NUMA systems to put pages nearer
210      to the processors accessing. The second is when allocating huge
211      pages as migration can relocate pages to satisfy a huge page
212      allocation instead of reclaiming.
213
214config PHYS_ADDR_T_64BIT
215    def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
216
217config ZONE_DMA_FLAG
218    int
219    default "0" if !ZONE_DMA
220    default "1"
221
222config BOUNCE
223    def_bool y
224    depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
225
226config NR_QUICK
227    int
228    depends on QUICKLIST
229    default "2" if AVR32
230    default "1"
231
232config VIRT_TO_BUS
233    def_bool y
234    depends on !ARCH_NO_VIRT_TO_BUS
235
236config MMU_NOTIFIER
237    bool
238
239config KSM
240    bool "Enable KSM for page merging"
241    depends on MMU
242    help
243      Enable Kernel Samepage Merging: KSM periodically scans those areas
244      of an application's address space that an app has advised may be
245      mergeable. When it finds pages of identical content, it replaces
246      the many instances by a single page with that content, so
247      saving memory until one or another app needs to modify the content.
248      Recommended for use with KVM, or with other duplicative applications.
249      See Documentation/vm/ksm.txt for more information: KSM is inactive
250      until a program has madvised that an area is MADV_MERGEABLE, and
251      root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
252
253config DEFAULT_MMAP_MIN_ADDR
254        int "Low address space to protect from user allocation"
255    depends on MMU
256        default 4096
257        help
258      This is the portion of low virtual memory which should be protected
259      from userspace allocation. Keeping a user from writing to low pages
260      can help reduce the impact of kernel NULL pointer bugs.
261
262      For most ia64, ppc64 and x86 users with lots of address space
263      a value of 65536 is reasonable and should cause no problems.
264      On arm and other archs it should not be higher than 32768.
265      Programs which use vm86 functionality or have some need to map
266      this low address space will need CAP_SYS_RAWIO or disable this
267      protection by setting the value to 0.
268
269      This value can be changed after boot using the
270      /proc/sys/vm/mmap_min_addr tunable.
271
272config ARCH_SUPPORTS_MEMORY_FAILURE
273    bool
274
275config MEMORY_FAILURE
276    depends on MMU
277    depends on ARCH_SUPPORTS_MEMORY_FAILURE
278    bool "Enable recovery from hardware memory errors"
279    select MEMORY_ISOLATION
280    help
281      Enables code to recover from some memory failures on systems
282      with MCA recovery. This allows a system to continue running
283      even when some of its memory has uncorrected errors. This requires
284      special hardware support and typically ECC memory.
285
286config HWPOISON_INJECT
287    tristate "HWPoison pages injector"
288    depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
289    select PROC_PAGE_MONITOR
290
291config NOMMU_INITIAL_TRIM_EXCESS
292    int "Turn on mmap() excess space trimming before booting"
293    depends on !MMU
294    default 1
295    help
296      The NOMMU mmap() frequently needs to allocate large contiguous chunks
297      of memory on which to store mappings, but it can only ask the system
298      allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
299      more than it requires. To deal with this, mmap() is able to trim off
300      the excess and return it to the allocator.
301
302      If trimming is enabled, the excess is trimmed off and returned to the
303      system allocator, which can cause extra fragmentation, particularly
304      if there are a lot of transient processes.
305
306      If trimming is disabled, the excess is kept, but not used, which for
307      long-term mappings means that the space is wasted.
308
309      Trimming can be dynamically controlled through a sysctl option
310      (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
311      excess pages there must be before trimming should occur, or zero if
312      no trimming is to occur.
313
314      This option specifies the initial value of this option. The default
315      of 1 says that all excess pages should be trimmed.
316
317      See Documentation/nommu-mmap.txt for more information.
318
319config TRANSPARENT_HUGEPAGE
320    bool "Transparent Hugepage Support"
321    depends on X86 && MMU
322    select COMPACTION
323    help
324      Transparent Hugepages allows the kernel to use huge pages and
325      huge tlb transparently to the applications whenever possible.
326      This feature can improve computing performance to certain
327      applications by speeding up page faults during memory
328      allocation, by reducing the number of tlb misses and by speeding
329      up the pagetable walking.
330
331      If memory constrained on embedded, you may want to say N.
332
333choice
334    prompt "Transparent Hugepage Support sysfs defaults"
335    depends on TRANSPARENT_HUGEPAGE
336    default TRANSPARENT_HUGEPAGE_ALWAYS
337    help
338      Selects the sysfs defaults for Transparent Hugepage Support.
339
340    config TRANSPARENT_HUGEPAGE_ALWAYS
341        bool "always"
342    help
343      Enabling Transparent Hugepage always, can increase the
344      memory footprint of applications without a guaranteed
345      benefit but it will work automatically for all applications.
346
347    config TRANSPARENT_HUGEPAGE_MADVISE
348        bool "madvise"
349    help
350      Enabling Transparent Hugepage madvise, will only provide a
351      performance improvement benefit to the applications using
352      madvise(MADV_HUGEPAGE) but it won't risk to increase the
353      memory footprint of applications without a guaranteed
354      benefit.
355endchoice
356
357config CROSS_MEMORY_ATTACH
358    bool "Cross Memory Support"
359    depends on MMU
360    default y
361    help
362      Enabling this option adds the system calls process_vm_readv and
363      process_vm_writev which allow a process with the correct privileges
364      to directly read from or write to to another process's address space.
365      See the man page for more details.
366
367#
368# UP and nommu archs use km based percpu allocator
369#
370config NEED_PER_CPU_KM
371    depends on !SMP
372    bool
373    default y
374
375config CLEANCACHE
376    bool "Enable cleancache driver to cache clean pages if tmem is present"
377    default n
378    help
379      Cleancache can be thought of as a page-granularity victim cache
380      for clean pages that the kernel's pageframe replacement algorithm
381      (PFRA) would like to keep around, but can't since there isn't enough
382      memory. So when the PFRA "evicts" a page, it first attempts to use
383      cleancache code to put the data contained in that page into
384      "transcendent memory", memory that is not directly accessible or
385      addressable by the kernel and is of unknown and possibly
386      time-varying size. And when a cleancache-enabled
387      filesystem wishes to access a page in a file on disk, it first
388      checks cleancache to see if it already contains it; if it does,
389      the page is copied into the kernel and a disk access is avoided.
390      When a transcendent memory driver is available (such as zcache or
391      Xen transcendent memory), a significant I/O reduction
392      may be achieved. When none is available, all cleancache calls
393      are reduced to a single pointer-compare-against-NULL resulting
394      in a negligible performance hit.
395
396      If unsure, say Y to enable cleancache
397
398config FRONTSWAP
399    bool "Enable frontswap to cache swap pages if tmem is present"
400    depends on SWAP
401    default n
402    help
403      Frontswap is so named because it can be thought of as the opposite
404      of a "backing" store for a swap device. The data is stored into
405      "transcendent memory", memory that is not directly accessible or
406      addressable by the kernel and is of unknown and possibly
407      time-varying size. When space in transcendent memory is available,
408      a significant swap I/O reduction may be achieved. When none is
409      available, all frontswap calls are reduced to a single pointer-
410      compare-against-NULL resulting in a negligible performance hit
411      and swap data is stored as normal on the matching swap device.
412
413      If unsure, say Y to enable frontswap.
414

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