mincore — determine whether pages are resident in memory
#include <unistd.h> #include <sys/mman.h>
int
mincore( |
void * | start, |
| size_t | length, | |
| unsigned char * | vec); |
mincore() returns a vector
that indicates whether pages of the calling process's virtual
memory are resident in core (RAM), and so will not cause a
disk access (page fault) if referenced. The kernel returns
residency information about the pages starting at the address
start, and continuing
for length bytes.
The start argument
must be a multiple of the system page size. The length argument need not be a
multiple of the page size, but since residency information is
returned for whole pages, length is effectively rounded
up to the next multiple of the page size. One may obtain the
page size (PAGE_SIZE) using sysconf(_SC_PAGESIZE).
The vec argument
must point to an array containing at least
(length+PAGE_SIZE-1) / PAGE_SIZE bytes. On return, the least
significant bit of each byte will be set if the corresponding
page is currently resident in memory, and be clear otherwise.
(The settings of the other bits in each byte are undefined;
these bits are reserved for possible later use.) Of course
the information returned in vec is only a snapshot: pages
that are not locked in memory can come and go at any moment,
and the contents of vec may already be stale by the
time this call returns.
On success, mincore()
returns zero. On error, −1 is returned, and
errno is set appropriately.
EAGAIN kernel is temporarily out of resources.
vec points
to an invalid address.
start is not
a multiple of the page size.
length is
greater than (TASK_SIZE
− start).
(This could occur if a negative value is specified for
length, 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.
start to
start +
length
contained unmapped memory.
Before kernel 2.6.21, mincore() did not return correct
information for MAP_PRIVATE
mappings, or for non-linear mappings (established using
remap_file_pages(2)).
mincore() is not specified
in POSIX.1-2001, and it is not available on all Unix
implementations.
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