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

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