MINCORE(2)

NAME
mincore - get information on whether pages are in core

SYNOPSIS
#include <unistd.h>
#include <sys/mman.h>

int mincore(void *start, size_t length, unsigned char *vec);

DESCRIPTION
The mincore function requests a vector describing which pages of a file are in core and can be read without disk access. The kernel will supply data for length bytes following the start address. On return, the kernel will have filled vec with bytes, of which the least significant bit indicates if a page is core resident. For mincore to return successfully, start must lie on a page boundary. It is the caller's responsibility to round up to the nearest page. The length parameter need not be a multiple of the page size. The vector vec must be large enough to contain (length+PAGE_SIZE-1) / PAGE_SIZE bytes. One may obtain the page size from getpagesize(2).

RETURN VALUE
On success, mincore returns zero. On error, -1 is returned, and errno is set appropriately.

ERRORS
EAGAIN kernel is temporarily out of resources

EINVAL
    start is not a multiple of the page size, or len has a non-positive value

EFAULT
    vec points to an invalid address

ENOMEM
    address to address + length contained unmapped memory, or memory not part of a file.

BUGS
mincore should return a bit vector and not a byte vector. As of Linux 2.4.20, it is not possible to gain information on the core residency of pages which are not backed by a file. In other words, calling mincore on a region returned by an anonymous mmap(2) specifying MAP_PRIVATE does not work and sets errno to ENOMEM. Unless pages are locked in memory, the contents of vec may be stale by the time they reach userspace.

CONFORMING TO
mincore does not appear to be part of POSIX or the Single Unix Specification.

HISTORY
The mincore() function first appeared in 4.4BSD.

AVAILABILITY
Since Linux 2.3.99pre1 and glibc 2.2.

SEE ALSO
getpagesize(2), mmap(2)