Function cachestat

pub unsafe fn cachestat(
    fd: u32,
    cstat_range: &mut cachestat_range_t,
    cstat: &mut cachestat_t,
    flags: u32,
) -> Result<(), i32> 

Available on crate feature dep_nc only.

cachestat() returns the page cache statistics of a file in the bytes range specified by off and len.

Number of cached pages, number of dirty pages, number of pages marked for writeback, number of evicted pages, and number of recently evicted pages.

An evicted page is a page that is previously in the page cache but has been evicted since. A page is recently evicted if its last eviction was recent enough that its reentry to the cache would indicate that it is actively being used by the system, and that there is memory pressure on the system.

off and len must be non-negative integers. If len > 0, the queried range is [off, off + len]. If len == 0, we will query in the range from off to the end of the file.

The flags argument is unused for now, but is included for future extensibility. User should pass 0 (i.e no flag specified).

Currently, hugetlbfs is not supported.

Because the status of a page can change after cachestat() checks it but before it returns to the application, the returned values may contain stale information.

return values:

• zero - success
• EFAULT - cstat or cstat_range points to an illegal address
• EINVAL - invalid flags
• EBADF - invalid file descriptor
• EOPNOTSUPP - file descriptor is of a hugetlbfs file