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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
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 
191 config MEMORY_HOTPLUG_SPARSE
192         def_bool y
193         depends on SPARSEMEM && MEMORY_HOTPLUG
194 
195 config MEMORY_HOTREMOVE
196         bool "Allow for memory hot remove"
197         select MEMORY_ISOLATION
198         select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
199         depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
200         depends on MIGRATION
201 
202 # Heavily threaded applications may benefit from splitting the mm-wide
203 # page_table_lock, so that faults on different parts of the user address
204 # space can be handled with less contention: split it at this NR_CPUS.
205 # Default to 4 for wider testing, though 8 might be more appropriate.
206 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
207 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
208 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
209 #
210 config SPLIT_PTLOCK_CPUS
211         int
212         default "999999" if !MMU
213         default "999999" if ARM && !CPU_CACHE_VIPT
214         default "999999" if PARISC && !PA20
215         default "4"
216 
217 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
218         bool
219 
220 #
221 # support for memory balloon
222 config MEMORY_BALLOON
223         bool
224 
225 #
226 # support for memory balloon compaction
227 config BALLOON_COMPACTION
228         bool "Allow for balloon memory compaction/migration"
229         def_bool y
230         depends on COMPACTION && MEMORY_BALLOON
231         help
232           Memory fragmentation introduced by ballooning might reduce
233           significantly the number of 2MB contiguous memory blocks that can be
234           used within a guest, thus imposing performance penalties associated
235           with the reduced number of transparent huge pages that could be used
236           by the guest workload. Allowing the compaction & migration for memory
237           pages enlisted as being part of memory balloon devices avoids the
238           scenario aforementioned and helps improving memory defragmentation.
239 
240 #
241 # support for memory compaction
242 config COMPACTION
243         bool "Allow for memory compaction"
244         def_bool y
245         select MIGRATION
246         depends on MMU
247         help
248           Allows the compaction of memory for the allocation of huge pages.
249 
250 #
251 # support for page migration
252 #
253 config MIGRATION
254         bool "Page migration"
255         def_bool y
256         depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
257         help
258           Allows the migration of the physical location of pages of processes
259           while the virtual addresses are not changed. This is useful in
260           two situations. The first is on NUMA systems to put pages nearer
261           to the processors accessing. The second is when allocating huge
262           pages as migration can relocate pages to satisfy a huge page
263           allocation instead of reclaiming.
264 
265 config ARCH_ENABLE_HUGEPAGE_MIGRATION
266         bool
267 
268 config PHYS_ADDR_T_64BIT
269         def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
270 
271 config ZONE_DMA_FLAG
272         int
273         default "0" if !ZONE_DMA
274         default "1"
275 
276 config BOUNCE
277         bool "Enable bounce buffers"
278         default y
279         depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
280         help
281           Enable bounce buffers for devices that cannot access
282           the full range of memory available to the CPU. Enabled
283           by default when ZONE_DMA or HIGHMEM is selected, but you
284           may say n to override this.
285 
286 # On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
287 # have more than 4GB of memory, but we don't currently use the IOTLB to present
288 # a 32-bit address to OHCI.  So we need to use a bounce pool instead.
289 config NEED_BOUNCE_POOL
290         bool
291         default y if TILE && USB_OHCI_HCD
292 
293 config NR_QUICK
294         int
295         depends on QUICKLIST
296         default "2" if AVR32
297         default "1"
298 
299 config VIRT_TO_BUS
300         bool
301         help
302           An architecture should select this if it implements the
303           deprecated interface virt_to_bus().  All new architectures
304           should probably not select this.
305 
306 
307 config MMU_NOTIFIER
308         bool
309         select SRCU
310 
311 config KSM
312         bool "Enable KSM for page merging"
313         depends on MMU
314         help
315           Enable Kernel Samepage Merging: KSM periodically scans those areas
316           of an application's address space that an app has advised may be
317           mergeable.  When it finds pages of identical content, it replaces
318           the many instances by a single page with that content, so
319           saving memory until one or another app needs to modify the content.
320           Recommended for use with KVM, or with other duplicative applications.
321           See Documentation/vm/ksm.txt for more information: KSM is inactive
322           until a program has madvised that an area is MADV_MERGEABLE, and
323           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
324 
325 config DEFAULT_MMAP_MIN_ADDR
326         int "Low address space to protect from user allocation"
327         depends on MMU
328         default 4096
329         help
330           This is the portion of low virtual memory which should be protected
331           from userspace allocation.  Keeping a user from writing to low pages
332           can help reduce the impact of kernel NULL pointer bugs.
333 
334           For most ia64, ppc64 and x86 users with lots of address space
335           a value of 65536 is reasonable and should cause no problems.
336           On arm and other archs it should not be higher than 32768.
337           Programs which use vm86 functionality or have some need to map
338           this low address space will need CAP_SYS_RAWIO or disable this
339           protection by setting the value to 0.
340 
341           This value can be changed after boot using the
342           /proc/sys/vm/mmap_min_addr tunable.
343 
344 config ARCH_SUPPORTS_MEMORY_FAILURE
345         bool
346 
347 config MEMORY_FAILURE
348         depends on MMU
349         depends on ARCH_SUPPORTS_MEMORY_FAILURE
350         bool "Enable recovery from hardware memory errors"
351         select MEMORY_ISOLATION
352         select RAS
353         help
354           Enables code to recover from some memory failures on systems
355           with MCA recovery. This allows a system to continue running
356           even when some of its memory has uncorrected errors. This requires
357           special hardware support and typically ECC memory.
358 
359 config HWPOISON_INJECT
360         tristate "HWPoison pages injector"
361         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
362         select PROC_PAGE_MONITOR
363 
364 config NOMMU_INITIAL_TRIM_EXCESS
365         int "Turn on mmap() excess space trimming before booting"
366         depends on !MMU
367         default 1
368         help
369           The NOMMU mmap() frequently needs to allocate large contiguous chunks
370           of memory on which to store mappings, but it can only ask the system
371           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
372           more than it requires.  To deal with this, mmap() is able to trim off
373           the excess and return it to the allocator.
374 
375           If trimming is enabled, the excess is trimmed off and returned to the
376           system allocator, which can cause extra fragmentation, particularly
377           if there are a lot of transient processes.
378 
379           If trimming is disabled, the excess is kept, but not used, which for
380           long-term mappings means that the space is wasted.
381 
382           Trimming can be dynamically controlled through a sysctl option
383           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
384           excess pages there must be before trimming should occur, or zero if
385           no trimming is to occur.
386 
387           This option specifies the initial value of this option.  The default
388           of 1 says that all excess pages should be trimmed.
389 
390           See Documentation/nommu-mmap.txt for more information.
391 
392 config TRANSPARENT_HUGEPAGE
393         bool "Transparent Hugepage Support"
394         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
395         select COMPACTION
396         help
397           Transparent Hugepages allows the kernel to use huge pages and
398           huge tlb transparently to the applications whenever possible.
399           This feature can improve computing performance to certain
400           applications by speeding up page faults during memory
401           allocation, by reducing the number of tlb misses and by speeding
402           up the pagetable walking.
403 
404           If memory constrained on embedded, you may want to say N.
405 
406 choice
407         prompt "Transparent Hugepage Support sysfs defaults"
408         depends on TRANSPARENT_HUGEPAGE
409         default TRANSPARENT_HUGEPAGE_ALWAYS
410         help
411           Selects the sysfs defaults for Transparent Hugepage Support.
412 
413         config TRANSPARENT_HUGEPAGE_ALWAYS
414                 bool "always"
415         help
416           Enabling Transparent Hugepage always, can increase the
417           memory footprint of applications without a guaranteed
418           benefit but it will work automatically for all applications.
419 
420         config TRANSPARENT_HUGEPAGE_MADVISE
421                 bool "madvise"
422         help
423           Enabling Transparent Hugepage madvise, will only provide a
424           performance improvement benefit to the applications using
425           madvise(MADV_HUGEPAGE) but it won't risk to increase the
426           memory footprint of applications without a guaranteed
427           benefit.
428 endchoice
429 
430 #
431 # UP and nommu archs use km based percpu allocator
432 #
433 config NEED_PER_CPU_KM
434         depends on !SMP
435         bool
436         default y
437 
438 config CLEANCACHE
439         bool "Enable cleancache driver to cache clean pages if tmem is present"
440         default n
441         help
442           Cleancache can be thought of as a page-granularity victim cache
443           for clean pages that the kernel's pageframe replacement algorithm
444           (PFRA) would like to keep around, but can't since there isn't enough
445           memory.  So when the PFRA "evicts" a page, it first attempts to use
446           cleancache code to put the data contained in that page into
447           "transcendent memory", memory that is not directly accessible or
448           addressable by the kernel and is of unknown and possibly
449           time-varying size.  And when a cleancache-enabled
450           filesystem wishes to access a page in a file on disk, it first
451           checks cleancache to see if it already contains it; if it does,
452           the page is copied into the kernel and a disk access is avoided.
453           When a transcendent memory driver is available (such as zcache or
454           Xen transcendent memory), a significant I/O reduction
455           may be achieved.  When none is available, all cleancache calls
456           are reduced to a single pointer-compare-against-NULL resulting
457           in a negligible performance hit.
458 
459           If unsure, say Y to enable cleancache
460 
461 config FRONTSWAP
462         bool "Enable frontswap to cache swap pages if tmem is present"
463         depends on SWAP
464         default n
465         help
466           Frontswap is so named because it can be thought of as the opposite
467           of a "backing" store for a swap device.  The data is stored into
468           "transcendent memory", memory that is not directly accessible or
469           addressable by the kernel and is of unknown and possibly
470           time-varying size.  When space in transcendent memory is available,
471           a significant swap I/O reduction may be achieved.  When none is
472           available, all frontswap calls are reduced to a single pointer-
473           compare-against-NULL resulting in a negligible performance hit
474           and swap data is stored as normal on the matching swap device.
475 
476           If unsure, say Y to enable frontswap.
477 
478 config CMA
479         bool "Contiguous Memory Allocator"
480         depends on HAVE_MEMBLOCK && MMU
481         select MIGRATION
482         select MEMORY_ISOLATION
483         help
484           This enables the Contiguous Memory Allocator which allows other
485           subsystems to allocate big physically-contiguous blocks of memory.
486           CMA reserves a region of memory and allows only movable pages to
487           be allocated from it. This way, the kernel can use the memory for
488           pagecache and when a subsystem requests for contiguous area, the
489           allocated pages are migrated away to serve the contiguous request.
490 
491           If unsure, say "n".
492 
493 config CMA_DEBUG
494         bool "CMA debug messages (DEVELOPMENT)"
495         depends on DEBUG_KERNEL && CMA
496         help
497           Turns on debug messages in CMA.  This produces KERN_DEBUG
498           messages for every CMA call as well as various messages while
499           processing calls such as dma_alloc_from_contiguous().
500           This option does not affect warning and error messages.
501 
502 config CMA_DEBUGFS
503         bool "CMA debugfs interface"
504         depends on CMA && DEBUG_FS
505         help
506           Turns on the DebugFS interface for CMA.
507 
508 config CMA_AREAS
509         int "Maximum count of the CMA areas"
510         depends on CMA
511         default 7
512         help
513           CMA allows to create CMA areas for particular purpose, mainly,
514           used as device private area. This parameter sets the maximum
515           number of CMA area in the system.
516 
517           If unsure, leave the default value "7".
518 
519 config MEM_SOFT_DIRTY
520         bool "Track memory changes"
521         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
522         select PROC_PAGE_MONITOR
523         help
524           This option enables memory changes tracking by introducing a
525           soft-dirty bit on pte-s. This bit it set when someone writes
526           into a page just as regular dirty bit, but unlike the latter
527           it can be cleared by hands.
528 
529           See Documentation/vm/soft-dirty.txt for more details.
530 
531 config ZSWAP
532         bool "Compressed cache for swap pages (EXPERIMENTAL)"
533         depends on FRONTSWAP && CRYPTO=y
534         select CRYPTO_LZO
535         select ZPOOL
536         default n
537         help
538           A lightweight compressed cache for swap pages.  It takes
539           pages that are in the process of being swapped out and attempts to
540           compress them into a dynamically allocated RAM-based memory pool.
541           This can result in a significant I/O reduction on swap device and,
542           in the case where decompressing from RAM is faster that swap device
543           reads, can also improve workload performance.
544 
545           This is marked experimental because it is a new feature (as of
546           v3.11) that interacts heavily with memory reclaim.  While these
547           interactions don't cause any known issues on simple memory setups,
548           they have not be fully explored on the large set of potential
549           configurations and workloads that exist.
550 
551 config ZPOOL
552         tristate "Common API for compressed memory storage"
553         default n
554         help
555           Compressed memory storage API.  This allows using either zbud or
556           zsmalloc.
557 
558 config ZBUD
559         tristate "Low density storage for compressed pages"
560         default n
561         help
562           A special purpose allocator for storing compressed pages.
563           It is designed to store up to two compressed pages per physical
564           page.  While this design limits storage density, it has simple and
565           deterministic reclaim properties that make it preferable to a higher
566           density approach when reclaim will be used.
567 
568 config ZSMALLOC
569         tristate "Memory allocator for compressed pages"
570         depends on MMU
571         default n
572         help
573           zsmalloc is a slab-based memory allocator designed to store
574           compressed RAM pages.  zsmalloc uses virtual memory mapping
575           in order to reduce fragmentation.  However, this results in a
576           non-standard allocator interface where a handle, not a pointer, is
577           returned by an alloc().  This handle must be mapped in order to
578           access the allocated space.
579 
580 config PGTABLE_MAPPING
581         bool "Use page table mapping to access object in zsmalloc"
582         depends on ZSMALLOC
583         help
584           By default, zsmalloc uses a copy-based object mapping method to
585           access allocations that span two pages. However, if a particular
586           architecture (ex, ARM) performs VM mapping faster than copying,
587           then you should select this. This causes zsmalloc to use page table
588           mapping rather than copying for object mapping.
589 
590           You can check speed with zsmalloc benchmark:
591           https://github.com/spartacus06/zsmapbench
592 
593 config ZSMALLOC_STAT
594         bool "Export zsmalloc statistics"
595         depends on ZSMALLOC
596         select DEBUG_FS
597         help
598           This option enables code in the zsmalloc to collect various
599           statistics about whats happening in zsmalloc and exports that
600           information to userspace via debugfs.
601           If unsure, say N.
602 
603 config GENERIC_EARLY_IOREMAP
604         bool
605 
606 config MAX_STACK_SIZE_MB
607         int "Maximum user stack size for 32-bit processes (MB)"
608         default 80
609         range 8 256 if METAG
610         range 8 2048
611         depends on STACK_GROWSUP && (!64BIT || COMPAT)
612         help
613           This is the maximum stack size in Megabytes in the VM layout of 32-bit
614           user processes when the stack grows upwards (currently only on parisc
615           and metag arch). The stack will be located at the highest memory
616           address minus the given value, unless the RLIMIT_STACK hard limit is
617           changed to a smaller value in which case that is used.
618 
619           A sane initial value is 80 MB.
620 
621 # For architectures that support deferred memory initialisation
622 config ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
623         bool
624 
625 config DEFERRED_STRUCT_PAGE_INIT
626         bool "Defer initialisation of struct pages to kthreads"
627         default n
628         depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
629         depends on MEMORY_HOTPLUG
630         help
631           Ordinarily all struct pages are initialised during early boot in a
632           single thread. On very large machines this can take a considerable
633           amount of time. If this option is set, large machines will bring up
634           a subset of memmap at boot and then initialise the rest in parallel
635           by starting one-off "pgdatinitX" kernel thread for each node X. This
636           has a potential performance impact on processes running early in the
637           lifetime of the system until these kthreads finish the
638           initialisation.
639 
640 config IDLE_PAGE_TRACKING
641         bool "Enable idle page tracking"
642         depends on SYSFS && MMU
643         select PAGE_EXTENSION if !64BIT
644         help
645           This feature allows to estimate the amount of user pages that have
646           not been touched during a given period of time. This information can
647           be useful to tune memory cgroup limits and/or for job placement
648           within a compute cluster.
649 
650           See Documentation/vm/idle_page_tracking.txt for more details.
651 
652 config ZONE_DEVICE
653         bool "Device memory (pmem, etc...) hotplug support" if EXPERT
654         depends on MEMORY_HOTPLUG
655         depends on MEMORY_HOTREMOVE
656         depends on SPARSEMEM_VMEMMAP
657         depends on X86_64 #arch_add_memory() comprehends device memory
658 
659         help
660           Device memory hotplug support allows for establishing pmem,
661           or other device driver discovered memory regions, in the
662           memmap. This allows pfn_to_page() lookups of otherwise
663           "device-physical" addresses which is needed for using a DAX
664           mapping in an O_DIRECT operation, among other things.
665 
666           If FS_DAX is enabled, then say Y.
667 
668 config FRAME_VECTOR
669         bool
670 
671 config ARCH_USES_HIGH_VMA_FLAGS
672         bool
673 config ARCH_HAS_PKEYS
674         bool

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