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Linux/mm/Kconfig

  1 config SELECT_MEMORY_MODEL
  2         def_bool y
  3         depends on ARCH_SELECT_MEMORY_MODEL
  4 
  5 choice
  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 
 12 config 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 a 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 
 31 config 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 
 47 config 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 
 62 endchoice
 63 
 64 config DISCONTIGMEM
 65         def_bool y
 66         depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
 67 
 68 config SPARSEMEM
 69         def_bool y
 70         depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
 71 
 72 config FLATMEM
 73         def_bool y
 74         depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
 75 
 76 config 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 #
 85 config NEED_MULTIPLE_NODES
 86         def_bool y
 87         depends on DISCONTIGMEM || NUMA
 88 
 89 config 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 #
103 config 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 #
111 config SPARSEMEM_EXTREME
112         def_bool y
113         depends on SPARSEMEM && !SPARSEMEM_STATIC
114 
115 config SPARSEMEM_VMEMMAP_ENABLE
116         bool
117 
118 config SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
119         def_bool y
120         depends on SPARSEMEM && X86_64
121 
122 config 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 
131 config HAVE_MEMBLOCK
132         boolean
133 
134 config HAVE_MEMBLOCK_NODE_MAP
135         boolean
136 
137 config HAVE_MEMBLOCK_PHYS_MAP
138         boolean
139 
140 config HAVE_GENERIC_RCU_GUP
141         boolean
142 
143 config ARCH_DISCARD_MEMBLOCK
144         boolean
145 
146 config NO_BOOTMEM
147         boolean
148 
149 config MEMORY_ISOLATION
150         boolean
151 
152 config MOVABLE_NODE
153         boolean "Enable to assign a node which has only movable memory"
154         depends on HAVE_MEMBLOCK
155         depends on NO_BOOTMEM
156         depends on X86_64
157         depends on NUMA
158         default n
159         help
160           Allow a node to have only movable memory.  Pages used by the kernel,
161           such as direct mapping pages cannot be migrated.  So the corresponding
162           memory device cannot be hotplugged.  This option allows the following
163           two things:
164           - When the system is booting, node full of hotpluggable memory can
165           be arranged to have only movable memory so that the whole node can
166           be hot-removed. (need movable_node boot option specified).
167           - After the system is up, the option allows users to online all the
168           memory of a node as movable memory so that the whole node can be
169           hot-removed.
170 
171           Users who don't use the memory hotplug feature are fine with this
172           option on since they don't specify movable_node boot option or they
173           don't online memory as movable.
174 
175           Say Y here if you want to hotplug a whole node.
176           Say N here if you want kernel to use memory on all nodes evenly.
177 
178 #
179 # Only be set on architectures that have completely implemented memory hotplug
180 # feature. If you are not sure, don't touch it.
181 #
182 config HAVE_BOOTMEM_INFO_NODE
183         def_bool n
184 
185 # eventually, we can have this option just 'select SPARSEMEM'
186 config MEMORY_HOTPLUG
187         bool "Allow for memory hot-add"
188         depends on SPARSEMEM || X86_64_ACPI_NUMA
189         depends on ARCH_ENABLE_MEMORY_HOTPLUG
190         depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
191 
192 config MEMORY_HOTPLUG_SPARSE
193         def_bool y
194         depends on SPARSEMEM && MEMORY_HOTPLUG
195 
196 config MEMORY_HOTREMOVE
197         bool "Allow for memory hot remove"
198         select MEMORY_ISOLATION
199         select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
200         depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
201         depends on MIGRATION
202 
203 #
204 # If we have space for more page flags then we can enable additional
205 # optimizations and functionality.
206 #
207 # Regular Sparsemem takes page flag bits for the sectionid if it does not
208 # use a virtual memmap. Disable extended page flags for 32 bit platforms
209 # that require the use of a sectionid in the page flags.
210 #
211 config PAGEFLAGS_EXTENDED
212         def_bool y
213         depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
214 
215 # Heavily threaded applications may benefit from splitting the mm-wide
216 # page_table_lock, so that faults on different parts of the user address
217 # space can be handled with less contention: split it at this NR_CPUS.
218 # Default to 4 for wider testing, though 8 might be more appropriate.
219 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
220 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
221 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
222 #
223 config SPLIT_PTLOCK_CPUS
224         int
225         default "999999" if !MMU
226         default "999999" if ARM && !CPU_CACHE_VIPT
227         default "999999" if PARISC && !PA20
228         default "4"
229 
230 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
231         boolean
232 
233 #
234 # support for memory balloon
235 config MEMORY_BALLOON
236         boolean
237 
238 #
239 # support for memory balloon compaction
240 config BALLOON_COMPACTION
241         bool "Allow for balloon memory compaction/migration"
242         def_bool y
243         depends on COMPACTION && MEMORY_BALLOON
244         help
245           Memory fragmentation introduced by ballooning might reduce
246           significantly the number of 2MB contiguous memory blocks that can be
247           used within a guest, thus imposing performance penalties associated
248           with the reduced number of transparent huge pages that could be used
249           by the guest workload. Allowing the compaction & migration for memory
250           pages enlisted as being part of memory balloon devices avoids the
251           scenario aforementioned and helps improving memory defragmentation.
252 
253 #
254 # support for memory compaction
255 config COMPACTION
256         bool "Allow for memory compaction"
257         def_bool y
258         select MIGRATION
259         depends on MMU
260         help
261           Allows the compaction of memory for the allocation of huge pages.
262 
263 #
264 # support for page migration
265 #
266 config MIGRATION
267         bool "Page migration"
268         def_bool y
269         depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
270         help
271           Allows the migration of the physical location of pages of processes
272           while the virtual addresses are not changed. This is useful in
273           two situations. The first is on NUMA systems to put pages nearer
274           to the processors accessing. The second is when allocating huge
275           pages as migration can relocate pages to satisfy a huge page
276           allocation instead of reclaiming.
277 
278 config ARCH_ENABLE_HUGEPAGE_MIGRATION
279         boolean
280 
281 config PHYS_ADDR_T_64BIT
282         def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
283 
284 config ZONE_DMA_FLAG
285         int
286         default "0" if !ZONE_DMA
287         default "1"
288 
289 config BOUNCE
290         bool "Enable bounce buffers"
291         default y
292         depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
293         help
294           Enable bounce buffers for devices that cannot access
295           the full range of memory available to the CPU. Enabled
296           by default when ZONE_DMA or HIGHMEM is selected, but you
297           may say n to override this.
298 
299 # On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
300 # have more than 4GB of memory, but we don't currently use the IOTLB to present
301 # a 32-bit address to OHCI.  So we need to use a bounce pool instead.
302 #
303 # We also use the bounce pool to provide stable page writes for jbd.  jbd
304 # initiates buffer writeback without locking the page or setting PG_writeback,
305 # and fixing that behavior (a second time; jbd2 doesn't have this problem) is
306 # a major rework effort.  Instead, use the bounce buffer to snapshot pages
307 # (until jbd goes away).  The only jbd user is ext3.
308 config NEED_BOUNCE_POOL
309         bool
310         default y if (TILE && USB_OHCI_HCD) || (BLK_DEV_INTEGRITY && JBD)
311 
312 config NR_QUICK
313         int
314         depends on QUICKLIST
315         default "2" if AVR32
316         default "1"
317 
318 config VIRT_TO_BUS
319         bool
320         help
321           An architecture should select this if it implements the
322           deprecated interface virt_to_bus().  All new architectures
323           should probably not select this.
324 
325 
326 config MMU_NOTIFIER
327         bool
328 
329 config KSM
330         bool "Enable KSM for page merging"
331         depends on MMU
332         help
333           Enable Kernel Samepage Merging: KSM periodically scans those areas
334           of an application's address space that an app has advised may be
335           mergeable.  When it finds pages of identical content, it replaces
336           the many instances by a single page with that content, so
337           saving memory until one or another app needs to modify the content.
338           Recommended for use with KVM, or with other duplicative applications.
339           See Documentation/vm/ksm.txt for more information: KSM is inactive
340           until a program has madvised that an area is MADV_MERGEABLE, and
341           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
342 
343 config DEFAULT_MMAP_MIN_ADDR
344         int "Low address space to protect from user allocation"
345         depends on MMU
346         default 4096
347         help
348           This is the portion of low virtual memory which should be protected
349           from userspace allocation.  Keeping a user from writing to low pages
350           can help reduce the impact of kernel NULL pointer bugs.
351 
352           For most ia64, ppc64 and x86 users with lots of address space
353           a value of 65536 is reasonable and should cause no problems.
354           On arm and other archs it should not be higher than 32768.
355           Programs which use vm86 functionality or have some need to map
356           this low address space will need CAP_SYS_RAWIO or disable this
357           protection by setting the value to 0.
358 
359           This value can be changed after boot using the
360           /proc/sys/vm/mmap_min_addr tunable.
361 
362 config ARCH_SUPPORTS_MEMORY_FAILURE
363         bool
364 
365 config MEMORY_FAILURE
366         depends on MMU
367         depends on ARCH_SUPPORTS_MEMORY_FAILURE
368         bool "Enable recovery from hardware memory errors"
369         select MEMORY_ISOLATION
370         help
371           Enables code to recover from some memory failures on systems
372           with MCA recovery. This allows a system to continue running
373           even when some of its memory has uncorrected errors. This requires
374           special hardware support and typically ECC memory.
375 
376 config HWPOISON_INJECT
377         tristate "HWPoison pages injector"
378         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
379         select PROC_PAGE_MONITOR
380 
381 config NOMMU_INITIAL_TRIM_EXCESS
382         int "Turn on mmap() excess space trimming before booting"
383         depends on !MMU
384         default 1
385         help
386           The NOMMU mmap() frequently needs to allocate large contiguous chunks
387           of memory on which to store mappings, but it can only ask the system
388           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
389           more than it requires.  To deal with this, mmap() is able to trim off
390           the excess and return it to the allocator.
391 
392           If trimming is enabled, the excess is trimmed off and returned to the
393           system allocator, which can cause extra fragmentation, particularly
394           if there are a lot of transient processes.
395 
396           If trimming is disabled, the excess is kept, but not used, which for
397           long-term mappings means that the space is wasted.
398 
399           Trimming can be dynamically controlled through a sysctl option
400           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
401           excess pages there must be before trimming should occur, or zero if
402           no trimming is to occur.
403 
404           This option specifies the initial value of this option.  The default
405           of 1 says that all excess pages should be trimmed.
406 
407           See Documentation/nommu-mmap.txt for more information.
408 
409 config TRANSPARENT_HUGEPAGE
410         bool "Transparent Hugepage Support"
411         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
412         select COMPACTION
413         help
414           Transparent Hugepages allows the kernel to use huge pages and
415           huge tlb transparently to the applications whenever possible.
416           This feature can improve computing performance to certain
417           applications by speeding up page faults during memory
418           allocation, by reducing the number of tlb misses and by speeding
419           up the pagetable walking.
420 
421           If memory constrained on embedded, you may want to say N.
422 
423 choice
424         prompt "Transparent Hugepage Support sysfs defaults"
425         depends on TRANSPARENT_HUGEPAGE
426         default TRANSPARENT_HUGEPAGE_ALWAYS
427         help
428           Selects the sysfs defaults for Transparent Hugepage Support.
429 
430         config TRANSPARENT_HUGEPAGE_ALWAYS
431                 bool "always"
432         help
433           Enabling Transparent Hugepage always, can increase the
434           memory footprint of applications without a guaranteed
435           benefit but it will work automatically for all applications.
436 
437         config TRANSPARENT_HUGEPAGE_MADVISE
438                 bool "madvise"
439         help
440           Enabling Transparent Hugepage madvise, will only provide a
441           performance improvement benefit to the applications using
442           madvise(MADV_HUGEPAGE) but it won't risk to increase the
443           memory footprint of applications without a guaranteed
444           benefit.
445 endchoice
446 
447 #
448 # UP and nommu archs use km based percpu allocator
449 #
450 config NEED_PER_CPU_KM
451         depends on !SMP
452         bool
453         default y
454 
455 config CLEANCACHE
456         bool "Enable cleancache driver to cache clean pages if tmem is present"
457         default n
458         help
459           Cleancache can be thought of as a page-granularity victim cache
460           for clean pages that the kernel's pageframe replacement algorithm
461           (PFRA) would like to keep around, but can't since there isn't enough
462           memory.  So when the PFRA "evicts" a page, it first attempts to use
463           cleancache code to put the data contained in that page into
464           "transcendent memory", memory that is not directly accessible or
465           addressable by the kernel and is of unknown and possibly
466           time-varying size.  And when a cleancache-enabled
467           filesystem wishes to access a page in a file on disk, it first
468           checks cleancache to see if it already contains it; if it does,
469           the page is copied into the kernel and a disk access is avoided.
470           When a transcendent memory driver is available (such as zcache or
471           Xen transcendent memory), a significant I/O reduction
472           may be achieved.  When none is available, all cleancache calls
473           are reduced to a single pointer-compare-against-NULL resulting
474           in a negligible performance hit.
475 
476           If unsure, say Y to enable cleancache
477 
478 config FRONTSWAP
479         bool "Enable frontswap to cache swap pages if tmem is present"
480         depends on SWAP
481         default n
482         help
483           Frontswap is so named because it can be thought of as the opposite
484           of a "backing" store for a swap device.  The data is stored into
485           "transcendent memory", memory that is not directly accessible or
486           addressable by the kernel and is of unknown and possibly
487           time-varying size.  When space in transcendent memory is available,
488           a significant swap I/O reduction may be achieved.  When none is
489           available, all frontswap calls are reduced to a single pointer-
490           compare-against-NULL resulting in a negligible performance hit
491           and swap data is stored as normal on the matching swap device.
492 
493           If unsure, say Y to enable frontswap.
494 
495 config CMA
496         bool "Contiguous Memory Allocator"
497         depends on HAVE_MEMBLOCK && MMU
498         select MIGRATION
499         select MEMORY_ISOLATION
500         help
501           This enables the Contiguous Memory Allocator which allows other
502           subsystems to allocate big physically-contiguous blocks of memory.
503           CMA reserves a region of memory and allows only movable pages to
504           be allocated from it. This way, the kernel can use the memory for
505           pagecache and when a subsystem requests for contiguous area, the
506           allocated pages are migrated away to serve the contiguous request.
507 
508           If unsure, say "n".
509 
510 config CMA_DEBUG
511         bool "CMA debug messages (DEVELOPMENT)"
512         depends on DEBUG_KERNEL && CMA
513         help
514           Turns on debug messages in CMA.  This produces KERN_DEBUG
515           messages for every CMA call as well as various messages while
516           processing calls such as dma_alloc_from_contiguous().
517           This option does not affect warning and error messages.
518 
519 config CMA_AREAS
520         int "Maximum count of the CMA areas"
521         depends on CMA
522         default 7
523         help
524           CMA allows to create CMA areas for particular purpose, mainly,
525           used as device private area. This parameter sets the maximum
526           number of CMA area in the system.
527 
528           If unsure, leave the default value "7".
529 
530 config MEM_SOFT_DIRTY
531         bool "Track memory changes"
532         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
533         select PROC_PAGE_MONITOR
534         help
535           This option enables memory changes tracking by introducing a
536           soft-dirty bit on pte-s. This bit it set when someone writes
537           into a page just as regular dirty bit, but unlike the latter
538           it can be cleared by hands.
539 
540           See Documentation/vm/soft-dirty.txt for more details.
541 
542 config ZSWAP
543         bool "Compressed cache for swap pages (EXPERIMENTAL)"
544         depends on FRONTSWAP && CRYPTO=y
545         select CRYPTO_LZO
546         select ZPOOL
547         default n
548         help
549           A lightweight compressed cache for swap pages.  It takes
550           pages that are in the process of being swapped out and attempts to
551           compress them into a dynamically allocated RAM-based memory pool.
552           This can result in a significant I/O reduction on swap device and,
553           in the case where decompressing from RAM is faster that swap device
554           reads, can also improve workload performance.
555 
556           This is marked experimental because it is a new feature (as of
557           v3.11) that interacts heavily with memory reclaim.  While these
558           interactions don't cause any known issues on simple memory setups,
559           they have not be fully explored on the large set of potential
560           configurations and workloads that exist.
561 
562 config ZPOOL
563         tristate "Common API for compressed memory storage"
564         default n
565         help
566           Compressed memory storage API.  This allows using either zbud or
567           zsmalloc.
568 
569 config ZBUD
570         tristate "Low density storage for compressed pages"
571         default n
572         help
573           A special purpose allocator for storing compressed pages.
574           It is designed to store up to two compressed pages per physical
575           page.  While this design limits storage density, it has simple and
576           deterministic reclaim properties that make it preferable to a higher
577           density approach when reclaim will be used.
578 
579 config ZSMALLOC
580         tristate "Memory allocator for compressed pages"
581         depends on MMU
582         default n
583         help
584           zsmalloc is a slab-based memory allocator designed to store
585           compressed RAM pages.  zsmalloc uses virtual memory mapping
586           in order to reduce fragmentation.  However, this results in a
587           non-standard allocator interface where a handle, not a pointer, is
588           returned by an alloc().  This handle must be mapped in order to
589           access the allocated space.
590 
591 config PGTABLE_MAPPING
592         bool "Use page table mapping to access object in zsmalloc"
593         depends on ZSMALLOC
594         help
595           By default, zsmalloc uses a copy-based object mapping method to
596           access allocations that span two pages. However, if a particular
597           architecture (ex, ARM) performs VM mapping faster than copying,
598           then you should select this. This causes zsmalloc to use page table
599           mapping rather than copying for object mapping.
600 
601           You can check speed with zsmalloc benchmark:
602           https://github.com/spartacus06/zsmapbench
603 
604 config GENERIC_EARLY_IOREMAP
605         bool
606 
607 config MAX_STACK_SIZE_MB
608         int "Maximum user stack size for 32-bit processes (MB)"
609         default 80
610         range 8 256 if METAG
611         range 8 2048
612         depends on STACK_GROWSUP && (!64BIT || COMPAT)
613         help
614           This is the maximum stack size in Megabytes in the VM layout of 32-bit
615           user processes when the stack grows upwards (currently only on parisc
616           and metag arch). The stack will be located at the highest memory
617           address minus the given value, unless the RLIMIT_STACK hard limit is
618           changed to a smaller value in which case that is used.
619 
620           A sane initial value is 80 MB.

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