cachestat
Section: System Calls (2)
Updated: 202-0-28
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NAME
cachestat - query the page cache statistics of a file
SYNOPSIS
#include <sys/mman.h>
int cachestat(unsigned int fd, struct cachestat_range *cstat_range,
struct cachestat *cstat, unsigned int flags);
struct cachestat_range {
__u64 off;
__u64 len;
};
struct cachestat {
__u64 nr_cache;
__u64 nr_dirty;
__u64 nr_writeback;
__u64 nr_evicted;
__u64 nr_recently_evicted;
};
DESCRIPTION
cachestat()
queries the number of cached pages, dirty pages,
pages marked for writeback, evicted pages,
and recently evicted pages in the byte range specified by
.off
and
.len
in the
cachestat_range
structure.
An evicted page is one that was previously in the page cache
but has since been evicted.
A page is considered recently evicted if its reentry into the cache
would indicate active usage under memory pressure.
The results are returned in a
cachestat
structure, pointed to by the
cstat
argument.
The
.off
and
.len
fields must be no-negative.
If
.len~>~0,
the queried range is
[
.off,~
.off+.len].
If
len~==~0,
the range is from
.off
to the end of the file.
The
flags
argument is reserved for future use and must be set to
0.
Currently,
hugetlbfs
files are not supported.
RETURN VALUE
On success,
cachestat()
returns 0.
On error, -1 is returned,
and
errno
is set to indicate the error.
ERRORS
- EFAULT
-
cstat
or
cstat_range
point to an invalid address.
- EINVAL
-
Invalid
flags
value.
- EBADF
-
Invalid file descriptor.
- EOPNOTSUPP
-
The file descriptor refers to a
hugetlbfs
file, which is unsupported.
STANDARDS
Linux.
HISTORY
Linux 6.5.
CAVEATS
Note that the status of a page may change after
cachestat()
retrieves it but before the values are returned to the application;
thus, the values may be slightly outdated.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- STANDARDS
-
- HISTORY
-
- CAVEATS
-
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