Section: Linux Programmer's Manual (3)
posix_madvise - give advice about patterns of memory usage
int posix_madvise(void *addr, size_t len, int advice);
Feature Test Macro Requirements for glibc (see
_POSIX_C_SOURCE >= 200112L
function allows an application to advise the system about its expected
patterns of usage of memory in the address range starting at
and continuing for
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
shall not affect the semantics of access to memory in the specified range.
argument is one of the following:
The application has no special advice regarding its memory usage patterns
for the specified address range.
This is the default behavior.
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.
The application expects to access the specified address range randomly.
Thus, read ahead may be less useful than normally.
The application expects to access the specified address range
in the near future.
Thus, read ahead may be beneficial.
The application expects that it will not access the specified address range
in the near future.
On failure, it returns a positive error number.
is not a multiple of the system page size or
Addresses in the specified range are partially or completely outside
the caller's address space.
first appeared in glibc version 2.2.
POSIX.1 permits an implementation to generate an error if
On Linux, specifying
as 0 is permitted (as a successful no-op).
In glibc, this function is implemented using
However, since glibc 2.6,
is treated as a no-op, because the corresponding
has destructive semantics.
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