Section (3) posix_madvise
posix_madvise — give advice about patterns of memory usage
allows an application to advise the system about its expected
patterns of usage of memory in the address range starting at
addr and continuing
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.
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.
addris not a multiple of the system page size or
Addresses in the specified range are partially or completely outside the caller_zsingle_quotesz_s address space.
POSIX.1 permits an implementation to generate an error if
len is 0. On Linux,
len as 0
is permitted (as a successful no-op).
In glibc, this function is implemented using madvise(2). However, since
is treated as a no-op, because the corresponding madvise(2) value,
MADV_DONTNEED, has destructive
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