MINCORE

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. (The other bits are undefined, reserved for possible later use.) Of course this is only a snapshot - pages that are not locked in core can come and go any moment, and the contents of vec may be stale already when this call returns.

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

Up to now (Linux 2.6.5), mincore does not return correct information for MAP_PRIVATE mappings.

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.