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1 .\" Copyright (C) 2001 David Gómez <davidge@jazzfree.com>
2 .\"
3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
4 .\"
5 .\" Based on comments from mm/filemap.c. Last modified on 10-06-2001
6 .\" Modified, 25 Feb 2002, Michael Kerrisk, <mtk.manpages@gmail.com>
7 .\" Added notes on MADV_DONTNEED
8 .\" 2010-06-19, mtk, Added documentation of MADV_MERGEABLE and
9 .\" MADV_UNMERGEABLE
10 .\" 2010-06-15, Andi Kleen, Add documentation of MADV_HWPOISON.
11 .\" 2010-06-19, Andi Kleen, Add documentation of MADV_SOFT_OFFLINE.
12 .\" 2011-09-18, Doug Goldstein <cardoe@cardoe.com>
13 .\" Document MADV_HUGEPAGE and MADV_NOHUGEPAGE
14 .\"
15 .TH MADVISE 2 2022-09-09 "Linux man-pages (unreleased)"
16 .SH NAME
17 madvise \- give advice about use of memory
18 .SH LIBRARY
19 Standard C library
20 .RI ( libc ", " \-lc )
21 .SH SYNOPSIS
22 .nf
23 .B #include <sys/mman.h>
24 .PP
25 .BI "int madvise(void *" addr ", size_t " length ", int " advice );
26 .fi
27 .PP
28 .RS -4
29 Feature Test Macro Requirements for glibc (see
30 .BR feature_test_macros (7)):
31 .RE
32 .PP
33 .BR madvise ():
34 .nf
35 Since glibc 2.19:
36 _DEFAULT_SOURCE
37 Up to and including glibc 2.19:
38 _BSD_SOURCE
39 .fi
40 .SH DESCRIPTION
41 The
42 .BR madvise ()
43 system call is used to give advice or directions to the kernel
44 about the address range beginning at address
45 .I addr
46 and with size
47 .IR length .
48 .BR madvise ()
49 only operates on whole pages, therefore
50 .I addr
51 must be page-aligned.
52 The value of
53 .I length
54 is rounded up to a multiple of page size.
55 In most cases,
56 the goal of such advice is to improve system or application performance.
57 .PP
58 Initially, the system call supported a set of "conventional"
59 .I advice
60 values, which are also available on several other implementations.
61 (Note, though, that
62 .BR madvise ()
63 is not specified in POSIX.)
64 Subsequently, a number of Linux-specific
65 .I advice
66 values have been added.
67 .\"
68 .\" ======================================================================
69 .\"
70 .SS Conventional advice values
71 The
72 .I advice
73 values listed below
74 allow an application to tell the kernel how it expects to use
75 some mapped or shared memory areas, so that the kernel can choose
76 appropriate read-ahead and caching techniques.
77 These
78 .I advice
79 values do not influence the semantics of the application
80 (except in the case of
81 .BR MADV_DONTNEED ),
82 but may influence its performance.
83 All of the
84 .I advice
85 values listed here have analogs in the POSIX-specified
86 .BR posix_madvise (3)
87 function, and the values have the same meanings, with the exception of
88 .BR MADV_DONTNEED .
89 .PP
90 The advice is indicated in the
91 .I advice
92 argument, which is one of the following:
93 .TP
94 .B MADV_NORMAL
95 No special treatment.
96 This is the default.
97 .TP
98 .B MADV_RANDOM
99 Expect page references in random order.
100 (Hence, read ahead may be less useful than normally.)
101 .TP
102 .B MADV_SEQUENTIAL
103 Expect page references in sequential order.
104 (Hence, pages in the given range can be aggressively read ahead,
105 and may be freed soon after they are accessed.)
106 .TP
107 .B MADV_WILLNEED
108 Expect access in the near future.
109 (Hence, it might be a good idea to read some pages ahead.)
110 .TP
111 .B MADV_DONTNEED
112 Do not expect access in the near future.
113 (For the time being, the application is finished with the given range,
114 so the kernel can free resources associated with it.)
115 .IP
116 After a successful
117 .B MADV_DONTNEED
118 operation,
119 the semantics of memory access in the specified region are changed:
120 subsequent accesses of pages in the range will succeed, but will result
121 in either repopulating the memory contents from the
122 up-to-date contents of the underlying mapped file
123 (for shared file mappings, shared anonymous mappings,
124 and shmem-based techniques such as System V shared memory segments)
125 or zero-fill-on-demand pages for anonymous private mappings.
126 .IP
127 Note that, when applied to shared mappings,
128 .B MADV_DONTNEED
129 might not lead to immediate freeing of the pages in the range.
130 The kernel is free to delay freeing the pages until an appropriate moment.
131 The resident set size (RSS) of the calling process will be immediately
132 reduced however.
133 .IP
134 .B MADV_DONTNEED
135 cannot be applied to locked pages, or
136 .B VM_PFNMAP
137 pages.
138 (Pages marked with the kernel-internal
139 .B VM_PFNMAP
140 .\" http://lwn.net/Articles/162860/
141 flag are special memory areas that are not managed
142 by the virtual memory subsystem.
143 Such pages are typically created by device drivers that
144 map the pages into user space.)
145 .IP
146 Support for Huge TLB pages was added in Linux v5.18.
147 Addresses within a mapping backed by Huge TLB pages must be aligned
148 to the underlying Huge TLB page size,
149 and the range length is rounded up
150 to a multiple of the underlying Huge TLB page size.
151 .\"
152 .\" ======================================================================
153 .\"
154 .SS Linux-specific advice values
155 The following Linux-specific
156 .I advice
157 values have no counterparts in the POSIX-specified
158 .BR posix_madvise (3),
159 and may or may not have counterparts in the
160 .BR madvise ()
161 interface available on other implementations.
162 Note that some of these operations change the semantics of memory accesses.
163 .TP
164 .BR MADV_REMOVE " (since Linux 2.6.16)"
165 .\" commit f6b3ec238d12c8cc6cc71490c6e3127988460349
166 Free up a given range of pages
167 and its associated backing store.
168 This is equivalent to punching a hole in the corresponding
169 range of the backing store (see
170 .BR fallocate (2)).
171 Subsequent accesses in the specified address range will see
172 data with a value of zero.
173 .\" Databases want to use this feature to drop a section of their
174 .\" bufferpool (shared memory segments) - without writing back to
175 .\" disk/swap space. This feature is also useful for supporting
176 .\" hot-plug memory on UML.
177 .IP
178 The specified address range must be mapped shared and writable.
179 This flag cannot be applied to locked pages, or
180 .B VM_PFNMAP
181 pages.
182 .IP
183 In the initial implementation, only
184 .BR tmpfs (5)
185 supported
186 .BR MADV_REMOVE ;
187 but since Linux 3.5,
188 .\" commit 3f31d07571eeea18a7d34db9af21d2285b807a17
189 any filesystem which supports the
190 .BR fallocate (2)
191 .B FALLOC_FL_PUNCH_HOLE
192 mode also supports
193 .BR MADV_REMOVE .
194 Filesystems which do not support
195 .B MADV_REMOVE
196 fail with the error
197 .BR EOPNOTSUPP .
198 .IP
199 Support for the Huge TLB filesystem was added in Linux v4.3.
200 .TP
201 .BR MADV_DONTFORK " (since Linux 2.6.16)"
202 .\" commit f822566165dd46ff5de9bf895cfa6c51f53bb0c4
203 .\" See http://lwn.net/Articles/171941/
204 Do not make the pages in this range available to the child after a
205 .BR fork (2).
206 This is useful to prevent copy-on-write semantics from changing
207 the physical location of a page if the parent writes to it after a
208 .BR fork (2).
209 (Such page relocations cause problems for hardware that
210 DMAs into the page.)
211 .\" [PATCH] madvise MADV_DONTFORK/MADV_DOFORK
212 .\" Currently, copy-on-write may change the physical address of
213 .\" a page even if the user requested that the page is pinned in
214 .\" memory (either by mlock or by get_user_pages). This happens
215 .\" if the process forks meanwhile, and the parent writes to that
216 .\" page. As a result, the page is orphaned: in case of
217 .\" get_user_pages, the application will never see any data hardware
218 .\" DMA's into this page after the COW. In case of mlock'd memory,
219 .\" the parent is not getting the realtime/security benefits of mlock.
220 .\"
221 .\" In particular, this affects the Infiniband modules which do DMA from
222 .\" and into user pages all the time.
223 .\"
224 .\" This patch adds madvise options to control whether memory range is
225 .\" inherited across fork. Useful e.g. for when hardware is doing DMA
226 .\" from/into these pages. Could also be useful to an application
227 .\" wanting to speed up its forks by cutting large areas out of
228 .\" consideration.
229 .\"
230 .\" SEE ALSO: http://lwn.net/Articles/171941/
231 .\" "Tweaks to madvise() and posix_fadvise()", 14 Feb 2006
232 .TP
233 .BR MADV_DOFORK " (since Linux 2.6.16)"
234 Undo the effect of
235 .BR MADV_DONTFORK ,
236 restoring the default behavior, whereby a mapping is inherited across
237 .BR fork (2).
238 .TP
239 .BR MADV_HWPOISON " (since Linux 2.6.32)"
240 .\" commit 9893e49d64a4874ea67849ee2cfbf3f3d6817573
241 Poison the pages in the range specified by
242 .I addr
243 and
244 .I length
245 and handle subsequent references to those pages
246 like a hardware memory corruption.
247 This operation is available only for privileged
248 .RB ( CAP_SYS_ADMIN )
249 processes.
250 This operation may result in the calling process receiving a
251 .B SIGBUS
252 and the page being unmapped.
253 .IP
254 This feature is intended for testing of memory error-handling code;
255 it is available only if the kernel was configured with
256 .BR CONFIG_MEMORY_FAILURE .
257 .TP
258 .BR MADV_MERGEABLE " (since Linux 2.6.32)"
259 .\" commit f8af4da3b4c14e7267c4ffb952079af3912c51c5
260 Enable Kernel Samepage Merging (KSM) for the pages in the range specified by
261 .I addr
262 and
263 .IR length .
264 The kernel regularly scans those areas of user memory that have
265 been marked as mergeable,
266 looking for pages with identical content.
267 These are replaced by a single write-protected page (which is automatically
268 copied if a process later wants to update the content of the page).
269 KSM merges only private anonymous pages (see
270 .BR mmap (2)).
271 .IP
272 The KSM feature is intended for applications that generate many
273 instances of the same data (e.g., virtualization systems such as KVM).
274 It can consume a lot of processing power; use with care.
275 See the Linux kernel source file
276 .I Documentation/admin\-guide/mm/ksm.rst
277 for more details.
278 .IP
279 The
280 .B MADV_MERGEABLE
281 and
282 .B MADV_UNMERGEABLE
283 operations are available only if the kernel was configured with
284 .BR CONFIG_KSM .
285 .TP
286 .BR MADV_UNMERGEABLE " (since Linux 2.6.32)"
287 Undo the effect of an earlier
288 .B MADV_MERGEABLE
289 operation on the specified address range;
290 KSM unmerges whatever pages it had merged in the address range specified by
291 .I addr
292 and
293 .IR length .
294 .TP
295 .BR MADV_SOFT_OFFLINE " (since Linux 2.6.33)"
296 .\" commit afcf938ee0aac4ef95b1a23bac704c6fbeb26de6
297 Soft offline the pages in the range specified by
298 .I addr
299 and
300 .IR length .
301 The memory of each page in the specified range is preserved
302 (i.e., when next accessed, the same content will be visible,
303 but in a new physical page frame),
304 and the original page is offlined
305 (i.e., no longer used, and taken out of normal memory management).
306 The effect of the
307 .B MADV_SOFT_OFFLINE
308 operation is invisible to (i.e., does not change the semantics of)
309 the calling process.
310 .IP
311 This feature is intended for testing of memory error-handling code;
312 it is available only if the kernel was configured with
313 .BR CONFIG_MEMORY_FAILURE .
314 .TP
315 .BR MADV_HUGEPAGE " (since Linux 2.6.38)"
316 .\" commit 0af4e98b6b095c74588af04872f83d333c958c32
317 .\" http://lwn.net/Articles/358904/
318 .\" https://lwn.net/Articles/423584/
319 Enable Transparent Huge Pages (THP) for pages in the range specified by
320 .I addr
321 and
322 .IR length .
323 Currently, Transparent Huge Pages work only with private anonymous pages (see
324 .BR mmap (2)).
325 The kernel will regularly scan the areas marked as huge page candidates
326 to replace them with huge pages.
327 The kernel will also allocate huge pages directly when the region is
328 naturally aligned to the huge page size (see
329 .BR posix_memalign (2)).
330 .IP
331 This feature is primarily aimed at applications that use large mappings of
332 data and access large regions of that memory at a time (e.g., virtualization
333 systems such as QEMU).
334 It can very easily waste memory (e.g., a 2\ MB mapping that only ever accesses
335 1 byte will result in 2\ MB of wired memory instead of one 4\ KB page).
336 See the Linux kernel source file
337 .I Documentation/admin\-guide/mm/transhuge.rst
338 for more details.
339 .IP
340 Most common kernels configurations provide
341 .BR MADV_HUGEPAGE -style
342 behavior by default, and thus
343 .B MADV_HUGEPAGE
344 is normally not necessary.
345 It is mostly intended for embedded systems, where
346 .BR MADV_HUGEPAGE -style
347 behavior may not be enabled by default in the kernel.
348 On such systems,
349 this flag can be used in order to selectively enable THP.
350 Whenever
351 .B MADV_HUGEPAGE
352 is used, it should always be in regions of memory with
353 an access pattern that the developer knows in advance won't risk
354 to increase the memory footprint of the application when transparent
355 hugepages are enabled.
356 .IP
357 The
358 .B MADV_HUGEPAGE
359 and
360 .B MADV_NOHUGEPAGE
361 operations are available only if the kernel was configured with
362 .BR CONFIG_TRANSPARENT_HUGEPAGE .
363 .TP
364 .BR MADV_NOHUGEPAGE " (since Linux 2.6.38)"
365 Ensures that memory in the address range specified by
366 .I addr
367 and
368 .I length
369 will not be backed by transparent hugepages.
370 .TP
371 .BR MADV_DONTDUMP " (since Linux 3.4)"
372 .\" commit 909af768e88867016f427264ae39d27a57b6a8ed
373 .\" commit accb61fe7bb0f5c2a4102239e4981650f9048519
374 Exclude from a core dump those pages in the range specified by
375 .I addr
376 and
377 .IR length .
378 This is useful in applications that have large areas of memory
379 that are known not to be useful in a core dump.
380 The effect of
381 .B MADV_DONTDUMP
382 takes precedence over the bit mask that is set via the
383 .I /proc/[pid]/coredump_filter
384 file (see
385 .BR core (5)).
386 .TP
387 .BR MADV_DODUMP " (since Linux 3.4)"
388 Undo the effect of an earlier
389 .BR MADV_DONTDUMP .
390 .TP
391 .BR MADV_FREE " (since Linux 4.5)"
392 The application no longer requires the pages in the range specified by
393 .I addr
394 and
395 .IR len .
396 The kernel can thus free these pages,
397 but the freeing could be delayed until memory pressure occurs.
398 For each of the pages that has been marked to be freed
399 but has not yet been freed,
400 the free operation will be canceled if the caller writes into the page.
401 After a successful
402 .B MADV_FREE
403 operation, any stale data (i.e., dirty, unwritten pages) will be lost
404 when the kernel frees the pages.
405 However, subsequent writes to pages in the range will succeed
406 and then kernel cannot free those dirtied pages,
407 so that the caller can always see just written data.
408 If there is no subsequent write,
409 the kernel can free the pages at any time.
410 Once pages in the range have been freed, the caller will
411 see zero-fill-on-demand pages upon subsequent page references.
412 .IP
413 The
414 .B MADV_FREE
415 operation
416 can be applied only to private anonymous pages (see
417 .BR mmap (2)).
418 In Linux before version 4.12,
419 .\" commit 93e06c7a645343d222c9a838834a51042eebbbf7
420 when freeing pages on a swapless system,
421 the pages in the given range are freed instantly,
422 regardless of memory pressure.
423 .TP
424 .BR MADV_WIPEONFORK " (since Linux 4.14)"
425 .\" commit d2cd9ede6e193dd7d88b6d27399e96229a551b19
426 Present the child process with zero-filled memory in this range after a
427 .BR fork (2).
428 This is useful in forking servers in order to ensure
429 that sensitive per-process data
430 (for example, PRNG seeds, cryptographic secrets, and so on)
431 is not handed to child processes.
432 .IP
433 The
434 .B MADV_WIPEONFORK
435 operation can be applied only to private anonymous pages (see
436 .BR mmap (2)).
437 .IP
438 Within the child created by
439 .BR fork (2),
440 the
441 .B MADV_WIPEONFORK
442 setting remains in place on the specified address range.
443 This setting is cleared during
444 .BR execve (2).
445 .TP
446 .BR MADV_KEEPONFORK " (since Linux 4.14)"
447 .\" commit d2cd9ede6e193dd7d88b6d27399e96229a551b19
448 Undo the effect of an earlier
449 .BR MADV_WIPEONFORK .
450 .TP
451 .BR MADV_COLD " (since Linux 5.4)"
452 .\" commit 9c276cc65a58faf98be8e56962745ec99ab87636
453 Deactivate a given range of pages.
454 This will make the pages a more probable
455 reclaim target should there be a memory pressure.
456 This is a nondestructive operation.
457 The advice might be ignored for some pages in the range when it is not
458 applicable.
459 .TP
460 .BR MADV_PAGEOUT " (since Linux 5.4)"
461 .\" commit 1a4e58cce84ee88129d5d49c064bd2852b481357
462 Reclaim a given range of pages.
463 This is done to free up memory occupied by these pages.
464 If a page is anonymous, it will be swapped out.
465 If a page is file-backed and dirty, it will be written back to the backing
466 storage.
467 The advice might be ignored for some pages in the range when it is not
468 applicable.
469 .TP
470 .BR MADV_POPULATE_READ " (since Linux 5.14)"
471 "Populate (prefault) page tables readable,
472 faulting in all pages in the range just as if manually reading from each page;
473 however,
474 avoid the actual memory access that would have been performed after handling
475 the fault.
476 .IP
477 In contrast to
478 .BR MAP_POPULATE ,
479 .B MADV_POPULATE_READ
480 does not hide errors,
481 can be applied to (parts of) existing mappings and will always populate
482 (prefault) page tables readable.
483 One example use case is prefaulting a file mapping,
484 reading all file content from disk;
485 however,
486 pages won't be dirtied and consequently won't have to be written back to disk
487 when evicting the pages from memory.
488 .IP
489 Depending on the underlying mapping,
490 map the shared zeropage,
491 preallocate memory or read the underlying file;
492 files with holes might or might not preallocate blocks.
493 If populating fails,
494 a
495 .B SIGBUS
496 signal is not generated; instead, an error is returned.
497 .IP
498 If
499 .B MADV_POPULATE_READ
500 succeeds,
501 all page tables have been populated (prefaulted) readable once.
502 If
503 .B MADV_POPULATE_READ
504 fails,
505 some page tables might have been populated.
506 .IP
507 .B MADV_POPULATE_READ
508 cannot be applied to mappings without read permissions
509 and special mappings,
510 for example,
511 mappings marked with kernel-internal flags such as
512 .B VM_PFNMAP
513 or
514 .BR VM_IO ,
515 or secret memory regions created using
516 .BR memfd_secret(2) .
517 .IP
518 Note that with
519 .BR MADV_POPULATE_READ ,
520 the process can be killed at any moment when the system runs out of memory.
521 .TP
522 .BR MADV_POPULATE_WRITE " (since Linux 5.14)"
523 Populate (prefault) page tables writable,
524 faulting in all pages in the range just as if manually writing to each
525 each page;
526 however,
527 avoid the actual memory access that would have been performed after handling
528 the fault.
529 .IP
530 In contrast to
531 .BR MAP_POPULATE ,
532 MADV_POPULATE_WRITE does not hide errors,
533 can be applied to (parts of) existing mappings and will always populate
534 (prefault) page tables writable.
535 One example use case is preallocating memory,
536 breaking any CoW (Copy on Write).
537 .IP
538 Depending on the underlying mapping,
539 preallocate memory or read the underlying file;
540 files with holes will preallocate blocks.
541 If populating fails,
542 a
543 .B SIGBUS
544 signal is not generated; instead, an error is returned.
545 .IP
546 If
547 .B MADV_POPULATE_WRITE
548 succeeds,
549 all page tables have been populated (prefaulted) writable once.
550 If
551 .B MADV_POPULATE_WRITE
552 fails,
553 some page tables might have been populated.
554 .IP
555 .B MADV_POPULATE_WRITE
556 cannot be applied to mappings without write permissions
557 and special mappings,
558 for example,
559 mappings marked with kernel-internal flags such as
560 .B VM_PFNMAP
561 or
562 .BR VM_IO ,
563 or secret memory regions created using
564 .BR memfd_secret(2) .
565 .IP
566 Note that with
567 .BR MADV_POPULATE_WRITE ,
568 the process can be killed at any moment when the system runs out of memory.
569 .SH RETURN VALUE
570 On success,
571 .BR madvise ()
572 returns zero.
573 On error, it returns \-1 and
574 .I errno
575 is set to indicate the error.
576 .SH ERRORS
577 .TP
578 .B EACCES
579 .I advice
580 is
581 .BR MADV_REMOVE ,
582 but the specified address range is not a shared writable mapping.
583 .TP
584 .B EAGAIN
585 A kernel resource was temporarily unavailable.
586 .TP
587 .B EBADF
588 The map exists, but the area maps something that isn't a file.
589 .TP
590 .B EFAULT
591 .I advice
592 is
593 .B MADV_POPULATE_READ
594 or
595 .BR MADV_POPULATE_WRITE ,
596 and populating (prefaulting) page tables failed because a
597 .B SIGBUS
598 would have been generated on actual memory access and the reason is not a
599 HW poisoned page
600 (HW poisoned pages can,
601 for example,
602 be created using the
603 .B MADV_HWPOISON
604 flag described elsewhere in this page).
605 .TP
606 .B EINVAL
607 .I addr
608 is not page-aligned or
609 .I length
610 is negative.
611 .\" .I length
612 .\" is zero,
613 .TP
614 .B EINVAL
615 .I advice
616 is not a valid.
617 .TP
618 .B EINVAL
619 .I advice
620 is
621 .B MADV_COLD
622 or
623 .B MADV_PAGEOUT
624 and the specified address range includes locked, Huge TLB pages, or
625 .B VM_PFNMAP
626 pages.
627 .TP
628 .B EINVAL
629 .I advice
630 is
631 .B MADV_DONTNEED
632 or
633 .B MADV_REMOVE
634 and the specified address range includes locked, Huge TLB pages, or
635 .B VM_PFNMAP
636 pages.
637 .TP
638 .B EINVAL
639 .I advice
640 is
641 .B MADV_MERGEABLE
642 or
643 .BR MADV_UNMERGEABLE ,
644 but the kernel was not configured with
645 .BR CONFIG_KSM .
646 .TP
647 .B EINVAL
648 .I advice
649 is
650 .B MADV_FREE
651 or
652 .B MADV_WIPEONFORK
653 but the specified address range includes file, Huge TLB,
654 .BR MAP_SHARED ,
655 or
656 .B VM_PFNMAP
657 ranges.
658 .TP
659 .B EINVAL
660 .I advice
661 is
662 .B MADV_POPULATE_READ
663 or
664 .BR MADV_POPULATE_WRITE ,
665 but the specified address range includes ranges with insufficient permissions
666 or special mappings,
667 for example,
668 mappings marked with kernel-internal flags such a
669 .B VM_IO
670 or
671 .BR VM_PFNMAP ,
672 or secret memory regions created using
673 .BR memfd_secret(2) .
674 .TP
675 .B EIO
676 (for
677 .BR MADV_WILLNEED )
678 Paging in this area would exceed the process's
679 maximum resident set size.
680 .TP
681 .B ENOMEM
682 (for
683 .BR MADV_WILLNEED )
684 Not enough memory: paging in failed.
685 .TP
686 .B ENOMEM
687 Addresses in the specified range are not currently
688 mapped, or are outside the address space of the process.
689 .TP
690 .B ENOMEM
691 .I advice
692 is
693 .B MADV_POPULATE_READ
694 or
695 .BR MADV_POPULATE_WRITE ,
696 and populating (prefaulting) page tables failed because there was not enough
697 memory.
698 .TP
699 .B EPERM
700 .I advice
701 is
702 .BR MADV_HWPOISON ,
703 but the caller does not have the
704 .B CAP_SYS_ADMIN
705 capability.
706 .TP
707 .B EHWPOISON
708 .I advice
709 is
710 .B MADV_POPULATE_READ
711 or
712 .BR MADV_POPULATE_WRITE ,
713 and populating (prefaulting) page tables failed because a HW poisoned page
714 (HW poisoned pages can,
715 for example,
716 be created using the
717 .B MADV_HWPOISON
718 flag described elsewhere in this page)
719 was encountered.
720 .SH VERSIONS
721 Since Linux 3.18,
722 .\" commit d3ac21cacc24790eb45d735769f35753f5b56ceb
723 support for this system call is optional,
724 depending on the setting of the
725 .B CONFIG_ADVISE_SYSCALLS
726 configuration option.
727 .SH STANDARDS
728 .BR madvise ()
729 is not specified by any standards.
730 Versions of this system call, implementing a wide variety of
731 .I advice
732 values, exist on many other implementations.
733 Other implementations typically implement at least the flags listed
734 above under
735 .IR "Conventional advice flags" ,
736 albeit with some variation in semantics.
737 .PP
738 POSIX.1-2001 describes
739 .BR posix_madvise (3)
740 with constants
741 .BR POSIX_MADV_NORMAL ,
742 .BR POSIX_MADV_RANDOM ,
743 .BR POSIX_MADV_SEQUENTIAL ,
744 .BR POSIX_MADV_WILLNEED ,
745 and
746 .BR POSIX_MADV_DONTNEED ,
747 and so on, with behavior close to the similarly named flags listed above.
748 .SH NOTES
749 .SS Linux notes
750 The Linux implementation requires that the address
751 .I addr
752 be page-aligned, and allows
753 .I length
754 to be zero.
755 If there are some parts of the specified address range
756 that are not mapped, the Linux version of
757 .BR madvise ()
758 ignores them and applies the call to the rest (but returns
759 .B ENOMEM
760 from the system call, as it should).
761 .\" .SH HISTORY
762 .\" The
763 .\" .BR madvise ()
764 .\" function first appeared in 4.4BSD.
765 .SH SEE ALSO
766 .BR getrlimit (2),
767 .BR memfd_secret (2),
768 .BR mincore (2),
769 .BR mmap (2),
770 .BR mprotect (2),
771 .BR msync (2),
772 .BR munmap (2),
773 .BR prctl (2),
774 .BR process_madvise (2),
775 .BR posix_madvise (3),
776 .BR core (5)