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

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