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mincore() - Unix, Linux System Call

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mincore - get information on whether pages are in core


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

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


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).


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


EAGAIN kernel is temporarily out of resources
EFAULT vec points to an invalid address
EINVAL start is not a multiple of the page size.
ENOMEM len is greater than (TASK_SIZE - start). (This could occur if a negative value is specified for len, since that value will be interpreted as a large unsigned integer.) In Linux 2.6.11 and earlier, the error EINVAL was returned for this condition.
ENOMEM address to address + length contained unmapped memory, or memory not part of a file.


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


mincore() is not specified in POSIX.1-2001, and it is not available on all Unix implementations.


The mincore() function first appeared in 4.4BSD.


Since Linux 2.3.99pre1 and glibc 2.2.


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