[PATCH v2] man/man2/cachestat.2: add a man page for cachestat()

[PATCH v2] man/man2/cachestat.2: add a man page for cachestat()

[Matteo Croce]

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 | 106 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 106 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..e7f60d935
--- /dev/null
+++ b/man/man2/cachestat.2
@@ -0,0 +1,106 @@
+.\" 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
+.nf
+.B #include <sys/mman.h>
+.PP
+.B struct cachestat_range {
+.BR "    __u64 off;"
+.BR "    __u64 len;"
+.RE
+.B };
+.PP
+.B struct cachestat {
+.BR "    __u64 nr_cache;"
+.BR "    __u64 nr_dirty;"
+.BR "    __u64 nr_writeback;"
+.BR "    __u64 nr_evicted;"
+.BR "    __u64 nr_recently_evicted;"
+.B };
+.PP
+.BI "int cachestat(unsigned int " fd ", struct cachestat_range *" cstat_range ","
+.br
+.BI "              struct cachestat *" cstat ", unsigned int " flags ");"
+.nf
+.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.
+.P
+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
+.RI [ .off ,\~ .off+.len ]
+. If
+.IR 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
+.BR 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
+point 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

Re: [PATCH v2] man/man2/cachestat.2: add a man page for cachestat()

[Alejandro Colomar]

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Hi Matteo,

On Mon, May 26, 2025 at 07:43:08PM +0200, Matteo Croce wrote:
> 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 | 106 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 106 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..e7f60d935
> --- /dev/null
> +++ b/man/man2/cachestat.2
> @@ -0,0 +1,106 @@
> +.\" 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
> +.nf
> +.B #include <sys/mman.h>
> +.PP

s/PP/P/g

> +.B struct cachestat_range {
> +.BR "    __u64 off;"

Since these lines only have 1 argument, s/BR/B/g.

See groff_man(7):

     .B [text]
            Set text in bold.  If no argument is given, a one‐line in‐
            put trap is planted; text on the next line, which can be
            further formatted with a macro, is set in bold.

     .BR bold‐text roman‐text ...
            Set each argument in bold and roman, alternately.

> +.BR "    __u64 len;"
> +.RE

This RE is spurious.

> +.B };
> +.PP
> +.B struct cachestat {
> +.BR "    __u64 nr_cache;"
> +.BR "    __u64 nr_dirty;"
> +.BR "    __u64 nr_writeback;"
> +.BR "    __u64 nr_evicted;"
> +.BR "    __u64 nr_recently_evicted;"
> +.B };
> +.PP
> +.BI "int cachestat(unsigned int " fd ", struct cachestat_range *" cstat_range ","
> +.br

This br is spurious.

> +.BI "              struct cachestat *" cstat ", unsigned int " flags ");"
> +.nf
> +.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.
> +.P
> +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

s/\. /.\n/

> +.I .len > 0
> +, the queried range is

The comma should go in the previous line.  Otherwise, it creates a
spurious space.

	.IR .len\~>\~0 ,

> +.RI [ .off ,\~ .off+.len ]
> +. If
> +.IR 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
> +.BR 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.

I'd move the paragraph from above to a CAVEATS section (see
man-pages(7)).

> +.SH RETURN VALUE
> +On success,
> +.B cachestat()
> +returns 0. On error, \-1 is returned and

s/\. /.\n/

s/ and/,\nand/

> +.I errno
> +is set appropriately.
> +.SH ERRORS
> +.TP
> +.B EFAULT
> +.I cstat
> +or
> +.I cstat_range
> +point 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.

Please add STANDARDS and HISTORY sections.  You can have a look at
membarrier(2) for this:

	$ man -w membarrier | xargs mansect '(STANDARDS|HISTORY)' | tail -n+3;
	.SH STANDARDS
	Linux.
	.SH HISTORY
	Linux 4.3.
	.P
	Before Linux 5.10, the prototype was:
	.P
	.in +4n
	.EX
	.BI "int membarrier(int " cmd ", int " flags );
	.EE
	.in

> -- 
> 2.49.0

Have a lovely day!
Alex

-- 
<https://www.alejandro-colomar.es/>

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