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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         bool
133 
134 config HAVE_MEMBLOCK_NODE_MAP
135         bool
136 
137 config HAVE_MEMBLOCK_PHYS_MAP
138         bool
139 
140 config HAVE_GENERIC_RCU_GUP
141         bool
142 
143 config ARCH_DISCARD_MEMBLOCK
144         bool
145 
146 config NO_BOOTMEM
147         bool
148 
149 config MEMORY_ISOLATION
150         bool
151 
152 config MOVABLE_NODE
153         bool "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 || OF_EARLY_FLATTREE || MEMORY_HOTPLUG
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 COMPILE_TEST || !KASAN
191 
192 config MEMORY_HOTPLUG_SPARSE
193         def_bool y
194         depends on SPARSEMEM && MEMORY_HOTPLUG
195 
196 config MEMORY_HOTPLUG_DEFAULT_ONLINE
197         bool "Online the newly added memory blocks by default"
198         default n
199         depends on MEMORY_HOTPLUG
200         help
201           This option sets the default policy setting for memory hotplug
202           onlining policy (/sys/devices/system/memory/auto_online_blocks) which
203           determines what happens to newly added memory regions. Policy setting
204           can always be changed at runtime.
205           See Documentation/memory-hotplug.txt for more information.
206 
207           Say Y here if you want all hot-plugged memory blocks to appear in
208           'online' state by default.
209           Say N here if you want the default policy to keep all hot-plugged
210           memory blocks in 'offline' state.
211 
212 config MEMORY_HOTREMOVE
213         bool "Allow for memory hot remove"
214         select MEMORY_ISOLATION
215         select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
216         depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
217         depends on MIGRATION
218 
219 # Heavily threaded applications may benefit from splitting the mm-wide
220 # page_table_lock, so that faults on different parts of the user address
221 # space can be handled with less contention: split it at this NR_CPUS.
222 # Default to 4 for wider testing, though 8 might be more appropriate.
223 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
224 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
225 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
226 #
227 config SPLIT_PTLOCK_CPUS
228         int
229         default "999999" if !MMU
230         default "999999" if ARM && !CPU_CACHE_VIPT
231         default "999999" if PARISC && !PA20
232         default "4"
233 
234 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
235         bool
236 
237 #
238 # support for memory balloon
239 config MEMORY_BALLOON
240         bool
241 
242 #
243 # support for memory balloon compaction
244 config BALLOON_COMPACTION
245         bool "Allow for balloon memory compaction/migration"
246         def_bool y
247         depends on COMPACTION && MEMORY_BALLOON
248         help
249           Memory fragmentation introduced by ballooning might reduce
250           significantly the number of 2MB contiguous memory blocks that can be
251           used within a guest, thus imposing performance penalties associated
252           with the reduced number of transparent huge pages that could be used
253           by the guest workload. Allowing the compaction & migration for memory
254           pages enlisted as being part of memory balloon devices avoids the
255           scenario aforementioned and helps improving memory defragmentation.
256 
257 #
258 # support for memory compaction
259 config COMPACTION
260         bool "Allow for memory compaction"
261         def_bool y
262         select MIGRATION
263         depends on MMU
264         help
265           Compaction is the only memory management component to form
266           high order (larger physically contiguous) memory blocks
267           reliably. The page allocator relies on compaction heavily and
268           the lack of the feature can lead to unexpected OOM killer
269           invocations for high order memory requests. You shouldn't
270           disable this option unless there really is a strong reason for
271           it and then we would be really interested to hear about that at
272           linux-mm@kvack.org.
273 
274 #
275 # support for page migration
276 #
277 config MIGRATION
278         bool "Page migration"
279         def_bool y
280         depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
281         help
282           Allows the migration of the physical location of pages of processes
283           while the virtual addresses are not changed. This is useful in
284           two situations. The first is on NUMA systems to put pages nearer
285           to the processors accessing. The second is when allocating huge
286           pages as migration can relocate pages to satisfy a huge page
287           allocation instead of reclaiming.
288 
289 config ARCH_ENABLE_HUGEPAGE_MIGRATION
290         bool
291 
292 config PHYS_ADDR_T_64BIT
293         def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
294 
295 config BOUNCE
296         bool "Enable bounce buffers"
297         default y
298         depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
299         help
300           Enable bounce buffers for devices that cannot access
301           the full range of memory available to the CPU. Enabled
302           by default when ZONE_DMA or HIGHMEM is selected, but you
303           may say n to override this.
304 
305 # On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
306 # have more than 4GB of memory, but we don't currently use the IOTLB to present
307 # a 32-bit address to OHCI.  So we need to use a bounce pool instead.
308 config NEED_BOUNCE_POOL
309         bool
310         default y if TILE && USB_OHCI_HCD
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         select SRCU
329 
330 config KSM
331         bool "Enable KSM for page merging"
332         depends on MMU
333         help
334           Enable Kernel Samepage Merging: KSM periodically scans those areas
335           of an application's address space that an app has advised may be
336           mergeable.  When it finds pages of identical content, it replaces
337           the many instances by a single page with that content, so
338           saving memory until one or another app needs to modify the content.
339           Recommended for use with KVM, or with other duplicative applications.
340           See Documentation/vm/ksm.txt for more information: KSM is inactive
341           until a program has madvised that an area is MADV_MERGEABLE, and
342           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
343 
344 config DEFAULT_MMAP_MIN_ADDR
345         int "Low address space to protect from user allocation"
346         depends on MMU
347         default 4096
348         help
349           This is the portion of low virtual memory which should be protected
350           from userspace allocation.  Keeping a user from writing to low pages
351           can help reduce the impact of kernel NULL pointer bugs.
352 
353           For most ia64, ppc64 and x86 users with lots of address space
354           a value of 65536 is reasonable and should cause no problems.
355           On arm and other archs it should not be higher than 32768.
356           Programs which use vm86 functionality or have some need to map
357           this low address space will need CAP_SYS_RAWIO or disable this
358           protection by setting the value to 0.
359 
360           This value can be changed after boot using the
361           /proc/sys/vm/mmap_min_addr tunable.
362 
363 config ARCH_SUPPORTS_MEMORY_FAILURE
364         bool
365 
366 config MEMORY_FAILURE
367         depends on MMU
368         depends on ARCH_SUPPORTS_MEMORY_FAILURE
369         bool "Enable recovery from hardware memory errors"
370         select MEMORY_ISOLATION
371         select RAS
372         help
373           Enables code to recover from some memory failures on systems
374           with MCA recovery. This allows a system to continue running
375           even when some of its memory has uncorrected errors. This requires
376           special hardware support and typically ECC memory.
377 
378 config HWPOISON_INJECT
379         tristate "HWPoison pages injector"
380         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
381         select PROC_PAGE_MONITOR
382 
383 config NOMMU_INITIAL_TRIM_EXCESS
384         int "Turn on mmap() excess space trimming before booting"
385         depends on !MMU
386         default 1
387         help
388           The NOMMU mmap() frequently needs to allocate large contiguous chunks
389           of memory on which to store mappings, but it can only ask the system
390           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
391           more than it requires.  To deal with this, mmap() is able to trim off
392           the excess and return it to the allocator.
393 
394           If trimming is enabled, the excess is trimmed off and returned to the
395           system allocator, which can cause extra fragmentation, particularly
396           if there are a lot of transient processes.
397 
398           If trimming is disabled, the excess is kept, but not used, which for
399           long-term mappings means that the space is wasted.
400 
401           Trimming can be dynamically controlled through a sysctl option
402           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
403           excess pages there must be before trimming should occur, or zero if
404           no trimming is to occur.
405 
406           This option specifies the initial value of this option.  The default
407           of 1 says that all excess pages should be trimmed.
408 
409           See Documentation/nommu-mmap.txt for more information.
410 
411 config TRANSPARENT_HUGEPAGE
412         bool "Transparent Hugepage Support"
413         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
414         select COMPACTION
415         select RADIX_TREE_MULTIORDER
416         help
417           Transparent Hugepages allows the kernel to use huge pages and
418           huge tlb transparently to the applications whenever possible.
419           This feature can improve computing performance to certain
420           applications by speeding up page faults during memory
421           allocation, by reducing the number of tlb misses and by speeding
422           up the pagetable walking.
423 
424           If memory constrained on embedded, you may want to say N.
425 
426 choice
427         prompt "Transparent Hugepage Support sysfs defaults"
428         depends on TRANSPARENT_HUGEPAGE
429         default TRANSPARENT_HUGEPAGE_ALWAYS
430         help
431           Selects the sysfs defaults for Transparent Hugepage Support.
432 
433         config TRANSPARENT_HUGEPAGE_ALWAYS
434                 bool "always"
435         help
436           Enabling Transparent Hugepage always, can increase the
437           memory footprint of applications without a guaranteed
438           benefit but it will work automatically for all applications.
439 
440         config TRANSPARENT_HUGEPAGE_MADVISE
441                 bool "madvise"
442         help
443           Enabling Transparent Hugepage madvise, will only provide a
444           performance improvement benefit to the applications using
445           madvise(MADV_HUGEPAGE) but it won't risk to increase the
446           memory footprint of applications without a guaranteed
447           benefit.
448 endchoice
449 
450 config  TRANSPARENT_HUGE_PAGECACHE
451         def_bool y
452         depends on TRANSPARENT_HUGEPAGE
453 
454 #
455 # UP and nommu archs use km based percpu allocator
456 #
457 config NEED_PER_CPU_KM
458         depends on !SMP
459         bool
460         default y
461 
462 config CLEANCACHE
463         bool "Enable cleancache driver to cache clean pages if tmem is present"
464         default n
465         help
466           Cleancache can be thought of as a page-granularity victim cache
467           for clean pages that the kernel's pageframe replacement algorithm
468           (PFRA) would like to keep around, but can't since there isn't enough
469           memory.  So when the PFRA "evicts" a page, it first attempts to use
470           cleancache code to put the data contained in that page into
471           "transcendent memory", memory that is not directly accessible or
472           addressable by the kernel and is of unknown and possibly
473           time-varying size.  And when a cleancache-enabled
474           filesystem wishes to access a page in a file on disk, it first
475           checks cleancache to see if it already contains it; if it does,
476           the page is copied into the kernel and a disk access is avoided.
477           When a transcendent memory driver is available (such as zcache or
478           Xen transcendent memory), a significant I/O reduction
479           may be achieved.  When none is available, all cleancache calls
480           are reduced to a single pointer-compare-against-NULL resulting
481           in a negligible performance hit.
482 
483           If unsure, say Y to enable cleancache
484 
485 config FRONTSWAP
486         bool "Enable frontswap to cache swap pages if tmem is present"
487         depends on SWAP
488         default n
489         help
490           Frontswap is so named because it can be thought of as the opposite
491           of a "backing" store for a swap device.  The data is stored into
492           "transcendent memory", memory that is not directly accessible or
493           addressable by the kernel and is of unknown and possibly
494           time-varying size.  When space in transcendent memory is available,
495           a significant swap I/O reduction may be achieved.  When none is
496           available, all frontswap calls are reduced to a single pointer-
497           compare-against-NULL resulting in a negligible performance hit
498           and swap data is stored as normal on the matching swap device.
499 
500           If unsure, say Y to enable frontswap.
501 
502 config CMA
503         bool "Contiguous Memory Allocator"
504         depends on HAVE_MEMBLOCK && MMU
505         select MIGRATION
506         select MEMORY_ISOLATION
507         help
508           This enables the Contiguous Memory Allocator which allows other
509           subsystems to allocate big physically-contiguous blocks of memory.
510           CMA reserves a region of memory and allows only movable pages to
511           be allocated from it. This way, the kernel can use the memory for
512           pagecache and when a subsystem requests for contiguous area, the
513           allocated pages are migrated away to serve the contiguous request.
514 
515           If unsure, say "n".
516 
517 config CMA_DEBUG
518         bool "CMA debug messages (DEVELOPMENT)"
519         depends on DEBUG_KERNEL && CMA
520         help
521           Turns on debug messages in CMA.  This produces KERN_DEBUG
522           messages for every CMA call as well as various messages while
523           processing calls such as dma_alloc_from_contiguous().
524           This option does not affect warning and error messages.
525 
526 config CMA_DEBUGFS
527         bool "CMA debugfs interface"
528         depends on CMA && DEBUG_FS
529         help
530           Turns on the DebugFS interface for CMA.
531 
532 config CMA_AREAS
533         int "Maximum count of the CMA areas"
534         depends on CMA
535         default 7
536         help
537           CMA allows to create CMA areas for particular purpose, mainly,
538           used as device private area. This parameter sets the maximum
539           number of CMA area in the system.
540 
541           If unsure, leave the default value "7".
542 
543 config MEM_SOFT_DIRTY
544         bool "Track memory changes"
545         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
546         select PROC_PAGE_MONITOR
547         help
548           This option enables memory changes tracking by introducing a
549           soft-dirty bit on pte-s. This bit it set when someone writes
550           into a page just as regular dirty bit, but unlike the latter
551           it can be cleared by hands.
552 
553           See Documentation/vm/soft-dirty.txt for more details.
554 
555 config ZSWAP
556         bool "Compressed cache for swap pages (EXPERIMENTAL)"
557         depends on FRONTSWAP && CRYPTO=y
558         select CRYPTO_LZO
559         select ZPOOL
560         default n
561         help
562           A lightweight compressed cache for swap pages.  It takes
563           pages that are in the process of being swapped out and attempts to
564           compress them into a dynamically allocated RAM-based memory pool.
565           This can result in a significant I/O reduction on swap device and,
566           in the case where decompressing from RAM is faster that swap device
567           reads, can also improve workload performance.
568 
569           This is marked experimental because it is a new feature (as of
570           v3.11) that interacts heavily with memory reclaim.  While these
571           interactions don't cause any known issues on simple memory setups,
572           they have not be fully explored on the large set of potential
573           configurations and workloads that exist.
574 
575 config ZPOOL
576         tristate "Common API for compressed memory storage"
577         default n
578         help
579           Compressed memory storage API.  This allows using either zbud or
580           zsmalloc.
581 
582 config ZBUD
583         tristate "Low (Up to 2x) density storage for compressed pages"
584         default n
585         help
586           A special purpose allocator for storing compressed pages.
587           It is designed to store up to two compressed pages per physical
588           page.  While this design limits storage density, it has simple and
589           deterministic reclaim properties that make it preferable to a higher
590           density approach when reclaim will be used.
591 
592 config Z3FOLD
593         tristate "Up to 3x density storage for compressed pages"
594         depends on ZPOOL
595         default n
596         help
597           A special purpose allocator for storing compressed pages.
598           It is designed to store up to three compressed pages per physical
599           page. It is a ZBUD derivative so the simplicity and determinism are
600           still there.
601 
602 config ZSMALLOC
603         tristate "Memory allocator for compressed pages"
604         depends on MMU
605         default n
606         help
607           zsmalloc is a slab-based memory allocator designed to store
608           compressed RAM pages.  zsmalloc uses virtual memory mapping
609           in order to reduce fragmentation.  However, this results in a
610           non-standard allocator interface where a handle, not a pointer, is
611           returned by an alloc().  This handle must be mapped in order to
612           access the allocated space.
613 
614 config PGTABLE_MAPPING
615         bool "Use page table mapping to access object in zsmalloc"
616         depends on ZSMALLOC
617         help
618           By default, zsmalloc uses a copy-based object mapping method to
619           access allocations that span two pages. However, if a particular
620           architecture (ex, ARM) performs VM mapping faster than copying,
621           then you should select this. This causes zsmalloc to use page table
622           mapping rather than copying for object mapping.
623 
624           You can check speed with zsmalloc benchmark:
625           https://github.com/spartacus06/zsmapbench
626 
627 config ZSMALLOC_STAT
628         bool "Export zsmalloc statistics"
629         depends on ZSMALLOC
630         select DEBUG_FS
631         help
632           This option enables code in the zsmalloc to collect various
633           statistics about whats happening in zsmalloc and exports that
634           information to userspace via debugfs.
635           If unsure, say N.
636 
637 config GENERIC_EARLY_IOREMAP
638         bool
639 
640 config MAX_STACK_SIZE_MB
641         int "Maximum user stack size for 32-bit processes (MB)"
642         default 80
643         range 8 256 if METAG
644         range 8 2048
645         depends on STACK_GROWSUP && (!64BIT || COMPAT)
646         help
647           This is the maximum stack size in Megabytes in the VM layout of 32-bit
648           user processes when the stack grows upwards (currently only on parisc
649           and metag arch). The stack will be located at the highest memory
650           address minus the given value, unless the RLIMIT_STACK hard limit is
651           changed to a smaller value in which case that is used.
652 
653           A sane initial value is 80 MB.
654 
655 # For architectures that support deferred memory initialisation
656 config ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
657         bool
658 
659 config DEFERRED_STRUCT_PAGE_INIT
660         bool "Defer initialisation of struct pages to kthreads"
661         default n
662         depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
663         depends on NO_BOOTMEM && MEMORY_HOTPLUG
664         depends on !FLATMEM
665         help
666           Ordinarily all struct pages are initialised during early boot in a
667           single thread. On very large machines this can take a considerable
668           amount of time. If this option is set, large machines will bring up
669           a subset of memmap at boot and then initialise the rest in parallel
670           by starting one-off "pgdatinitX" kernel thread for each node X. This
671           has a potential performance impact on processes running early in the
672           lifetime of the system until these kthreads finish the
673           initialisation.
674 
675 config IDLE_PAGE_TRACKING
676         bool "Enable idle page tracking"
677         depends on SYSFS && MMU
678         select PAGE_EXTENSION if !64BIT
679         help
680           This feature allows to estimate the amount of user pages that have
681           not been touched during a given period of time. This information can
682           be useful to tune memory cgroup limits and/or for job placement
683           within a compute cluster.
684 
685           See Documentation/vm/idle_page_tracking.txt for more details.
686 
687 config ZONE_DEVICE
688         bool "Device memory (pmem, etc...) hotplug support"
689         depends on MEMORY_HOTPLUG
690         depends on MEMORY_HOTREMOVE
691         depends on SPARSEMEM_VMEMMAP
692         depends on X86_64 #arch_add_memory() comprehends device memory
693 
694         help
695           Device memory hotplug support allows for establishing pmem,
696           or other device driver discovered memory regions, in the
697           memmap. This allows pfn_to_page() lookups of otherwise
698           "device-physical" addresses which is needed for using a DAX
699           mapping in an O_DIRECT operation, among other things.
700 
701           If FS_DAX is enabled, then say Y.
702 
703 config FRAME_VECTOR
704         bool
705 
706 config ARCH_USES_HIGH_VMA_FLAGS
707         bool
708 config ARCH_HAS_PKEYS
709         bool

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