[PATCH] man/man2/cachestat.2: add a man page for cachestat()

[Matteo Croce <technoboy85@gmail.com>]

From: Matteo Croce <teknoraver@meta.com>

Add a missing man page for cachestat().
The text was converted from the commit message:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cf264e1329fb0307e044f7675849f9f38b44c11a

Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Matteo Croce <teknoraver@meta.com>
---
 man/man2/cachestat.2 | 109 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 man/man2/cachestat.2

diff --git a/man/man2/cachestat.2 b/man/man2/cachestat.2
new file mode 100644
index 000000000..f741e3695
--- /dev/null
+++ b/man/man2/cachestat.2
@@ -0,0 +1,109 @@
+.\" Copyright, the authors of the Linux man-pages project
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.TH CACHESTAT 2 (date) "Linux man-pages (unreleased)"
+.SH NAME
+cachestat \- query the page cache statistics of a file
+.SH SYNOPSIS
+.B #include <sys/mman.h>
+.PP
+.B struct cachestat_range {
+.br
+.RS
+__u64 off;
+.br
+__u64 len;
+.RE
+.B };
+.PP
+.B struct cachestat {
+.br
+.RS
+__u64 nr_cache;
+.br
+__u64 nr_dirty;
+.br
+__u64 nr_writeback;
+.br
+__u64 nr_evicted;
+.br
+__u64 nr_recently_evicted;
+.RE
+.B };
+.PP
+.BI "int cachestat(unsigned int " fd ", struct cachestat_range *" cstat_range ","
+.br
+.BI "              struct cachestat *" cstat ", unsigned int " flags ");"
+.SH DESCRIPTION
+.B 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
+.I off
+and
+.I len
+in the
+.B cachestat_range
+structure.
+.PP
+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.
+.PP
+The results are returned in a
+.B cachestat
+structure, pointed to by the
+.I cstat
+argument.
+.PP
+The
+.I off
+and
+.I len
+fields must be non-negative. If
+.I len > 0
+, the queried range is
+.B [off, off + len]
+. If
+.I len == 0
+, the range is from
+.I off
+to the end of the file.
+.PP
+The
+.I flags
+argument is reserved for future use and must be set to
+.B 0
+.
+.PP
+Currently,
+.B hugetlbfs
+files are not supported.
+.PP
+Note that the status of a page may change after
+.B cachestat()
+retrieves it but before the values are returned to the application; thus, the values may be slightly outdated.
+.SH RETURN VALUE
+On success,
+.B cachestat()
+returns 0. On error, \-1 is returned and
+.I errno
+is set appropriately.
+.SH ERRORS
+.TP
+.B EFAULT
+.I cstat
+or
+.I cstat_range
+points to an invalid address.
+.TP
+.B EINVAL
+Invalid
+.I flags
+value.
+.TP
+.B EBADF
+Invalid file descriptor.
+.TP
+.B EOPNOTSUPP
+The file descriptor refers to a
+.B hugetlbfs
+file, which is unsupported.
-- 
2.49.0