дать совет о схемах использования памяти (give advice about patterns of memory usage)
Имя (Name)
posix_madvise - give advice about patterns of memory usage
Синопсис (Synopsis)
#include <sys/mman.h>
int posix_madvise(void *addr, size_t len, int advice);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
posix_madvise():
_POSIX_C_SOURCE >= 200112L
Описание (Description)
The posix_madvise() function allows an application to advise the
system about its expected patterns of usage of memory in the
address range starting at addr and continuing for len bytes. The
system is free to use this advice in order to improve the
performance of memory accesses (or to ignore the advice
altogether), but calling posix_madvise() shall not affect the
semantics of access to memory in the specified range.
The advice argument is one of the following:
POSIX_MADV_NORMAL
The application has no special advice regarding its memory
usage patterns for the specified address range. This is
the default behavior.
POSIX_MADV_SEQUENTIAL
The application expects to access the specified address
range sequentially, running from lower addresses to higher
addresses. Hence, pages in this region can be
aggressively read ahead, and may be freed soon after they
are accessed.
POSIX_MADV_RANDOM
The application expects to access the specified address
range randomly. Thus, read ahead may be less useful than
normally.
POSIX_MADV_WILLNEED
The application expects to access the specified address
range in the near future. Thus, read ahead may be
beneficial.
POSIX_MADV_DONTNEED
The application expects that it will not access the
specified address range in the near future.
Возвращаемое значение (Return value)
On success, posix_madvise() returns 0. On failure, it returns a
positive error number.
Ошибки (Error)
EINVAL addr is not a multiple of the system page size or len is
negative.
EINVAL advice is invalid.
ENOMEM Addresses in the specified range are partially or
completely outside the caller's address space.
Версии (Versions)
Support for posix_madvise() first appeared in glibc version 2.2.
Стандарты (Conforming to)
POSIX.1-2001.
Примечание (Note)
POSIX.1 permits an implementation to generate an error if len is
0. On Linux, specifying len as 0 is permitted (as a successful
no-op).
In glibc, this function is implemented using madvise(2).
However, since glibc 2.6, POSIX_MADV_DONTNEED is treated as a no-
op, because the corresponding madvise(2) value, MADV_DONTNEED,
has destructive semantics.
Смотри также (See also)
madvise(2), posix_fadvise(2)
