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

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