No special treatment. This is the default.

Expect page references in random order. (Hence, read ahead may be less useful than normally.)

Expect page references in sequential order. (Hence, pages in the given range can be aggressively read ahead, and may be freed soon after they are accessed.)

Expect access in the near future. (Hence, it might be a good idea to read some pages ahead.)

Do not expect access in the near future. (For the time being, the application is finished with the given range, so the kernel can free resources associated with it.) Subsequent accesses of pages in this range will succeed, but will result either in reloading of the memory contents from the underlying mapped file (see mmap(2)) or zero-fill-on-demand pages for mappings without an underlying file.

Free up a given range of pages and its associated backing store. Currently, only shmfs/tmpfs supports this; other file systems return with the error ENOSYS.

Do not make the pages in this range available to the child after a fork(2). This is useful to prevent copy-on-write semantics from changing the physical location of a page(s) if the parent writes to it after a fork(2). (Such page relocations cause problems for hardware that DMAs into the page(s).)

Undo the effect of MADV_DONTFORK, restoring the default behavior, whereby a mapping is inherited across fork(2).

Poison a page and handle it like a hardware memory corruption. This operation is only available for privileged (CAP_SYS_ADMIN) processes. This operation may result in the calling process receiving a SIGBUS and the page being unmapped. This feature is intended for testing of memory error-handling code; it is only available if the kernel was configured with CONFIG_MEMORY_FAILURE.

Soft offline the pages in the range specified by addr and length. The memory of each page in the specified range is preserved (i.e., when next accessed, the same content will be visible, but in a new physical page frame), and the original page is offlined (i.e., no longer used, and taken out of normal memory management). The effect of the MADV_SOFT_OFFLINE operation is invisible to (i.e., does not change the semantics of) the calling process. This feature is intended for testing of memory error-handling code; it is only available if the kernel was configured with CONFIG_MEMORY_FAILURE.

Enable Kernel Samepage Merging (KSM) for the pages in the range specified by addr and length. The kernel regularly scans those areas of user memory that have been marked as mergeable, looking for pages with identical content. These are replaced by a single write-protected page (which is automatically copied if a process later wants to update the content of the page). KSM only merges private anonymous pages (see mmap(2)). The KSM feature is intended for applications that generate many instances of the same data (e.g., virtualization systems such as KVM). It can consume a lot of processing power; use with care. See the kernel source file Documentation/vm/ksm.txt for more details. The MADV_MERGEABLE and MADV_UNMERGEABLE operations are only available if the kernel was configured with CONFIG_KSM.

Undo the effect of an earlier MADV_MERGEABLE operation on the specified address range; KSM unmerges whatever pages it had merged in the address range specified by addr and length.

Enables Transparent Huge Pages (THP) for pages in the range specified by addr and length. Currently, Transparent Huge Pages only work with private anonymous pages (see mmap(2)). The kernel will regularly scan the areas marked as huge page candidates to replace them with huge pages. The kernel will also allocate huge pages directly when the region is naturally aligned to the huge page size (see posix_memalign(2)). This feature is primarily aimed at applications that use large mappings of data and access large regions of that memory at a time (e.g. virtualization systems such as QEMU). It can very easily waste memory (e.g. a 2MB mapping that only ever accesses 1 byte will result in 2MB of wired memory instead of one 4KB page). See the kernel source file Documentation/vm/transhuge.txt for more details. The MADV_HUGEPAGE and MADV_NOHUGEPAGE operations are only available if the kernel was configured with CONFIG_TRANSPARENT_HUGEPAGE.

Ensures that memory in the address range specified by addr and length will not be collapsed into huge pages.

A kernel resource was temporarily unavailable.

The map exists, but the area maps something that isn't a file.

This error can occur for the following reasons:

(for MADV_WILLNEED) Paging in this area would exceed the process's maximum resident set size.

(for MADV_WILLNEED) Not enough memory: paging in failed.

Addresses in the specified range are not currently mapped, or are outside the address space of the process.