[PATCH v4] man/man2/cachestat.2: add a man page for cachestat()

[PATCH v4] 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 | 111 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 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..084d5cd04
--- /dev/null
+++ b/man/man2/cachestat.2
@@ -0,0 +1,111 @@
+.\" 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>
+.P
+.B struct cachestat_range {
+.B "    __u64 off;"
+.B "    __u64 len;"
+.B };
+.P
+.B struct cachestat {
+.B "    __u64 nr_cache;"
+.B "    __u64 nr_dirty;"
+.B "    __u64 nr_writeback;"
+.B "    __u64 nr_evicted;"
+.B "    __u64 nr_recently_evicted;"
+.B };
+.P
+.BI "int cachestat(unsigned int " fd ", struct cachestat_range *" cstat_range ","
+.BI "              struct cachestat *" cstat ", unsigned int " flags ");"
+.fi
+.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.
+.P
+The results are returned in a
+.B cachestat
+structure, pointed to by the
+.I cstat
+argument.
+.P
+The
+.I .off
+and
+.I .len
+fields must be non-negative.
+If
+.IR .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.
+.P
+The
+.I flags
+argument is reserved for future use and must be set to
+.BR 0 .
+.
+.P
+Currently,
+.B hugetlbfs
+files are not supported.
+.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.
+.SH STANDARDS
+Linux.
+.SH HISTORY
+Linux 6.5.
+.SH CAVEATS
+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.
-- 
2.49.0

Re: [PATCH v4] man/man2/cachestat.2: add a man page for cachestat()

[Alejandro Colomar]

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Hi Matteo,

On Wed, Jun 11, 2025 at 04:13:50PM +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>

Thanks!  I've applied the patch with a few amendments.  I've tweaked the
commit message too.  See below.
<https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=797d642cc47ff6f1b9199e5e1d28c528409e0c14>

> ---
>  man/man2/cachestat.2 | 111 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 111 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..084d5cd04
> --- /dev/null
> +++ b/man/man2/cachestat.2
> @@ -0,0 +1,111 @@
> +.\" 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>
> +.P
> +.B struct cachestat_range {
> +.B "    __u64 off;"
> +.B "    __u64 len;"
> +.B };
> +.P
> +.B struct cachestat {
> +.B "    __u64 nr_cache;"
> +.B "    __u64 nr_dirty;"
> +.B "    __u64 nr_writeback;"
> +.B "    __u64 nr_evicted;"
> +.B "    __u64 nr_recently_evicted;"
> +.B };

I've wrapped the structures in EX/EE, as is done in other pages.

I've also moved them after the function prototype, to have the function
stand out more.

> +.P
> +.BI "int cachestat(unsigned int " fd ", struct cachestat_range *" cstat_range ","
> +.BI "              struct cachestat *" cstat ", unsigned int " flags ");"
> +.fi
> +.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.
> +.P
> +The results are returned in a
> +.B cachestat
> +structure, pointed to by the
> +.I cstat
> +argument.
> +.P
> +The
> +.I .off
> +and
> +.I .len
> +fields must be non-negative.
> +If
> +.IR .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.
> +.P
> +The
> +.I flags
> +argument is reserved for future use and must be set to
> +.BR 0 .
> +.

I've removed the line above, since it doesn't do anything.

> +.P
> +Currently,
> +.B hugetlbfs
> +files are not supported.
> +.SH RETURN VALUE
> +On success,
> +.B cachestat()
> +returns 0.
> +On error, \-1 is returned,
> +and
> +.I errno
> +is set appropriately.

I've changed this sentence to be consistent with all other pages, which
say "is set to indicate the error".


Have a lovely day!
Alex

> +.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.
> +.SH STANDARDS
> +Linux.
> +.SH HISTORY
> +Linux 6.5.
> +.SH CAVEATS
> +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.
> -- 
> 2.49.0
> 
> 

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

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Re: [PATCH v4] man/man2/cachestat.2: add a man page for cachestat()

[Matteo Croce]

Il giorno gio 19 giu 2025 alle ore 02:16 Alejandro Colomar
<alx@kernel.org> ha scritto:
>
> Hi Matteo,
>
> On Wed, Jun 11, 2025 at 04:13:50PM +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>
>
> Thanks!  I've applied the patch with a few amendments.  I've tweaked the
> commit message too.  See below.
> <https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=797d642cc47ff6f1b9199e5e1d28c528409e0c14>
>

Got it, it's even better now. Thanks!

> > ---
> >  man/man2/cachestat.2 | 111 +++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 111 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..084d5cd04
> > --- /dev/null
> > +++ b/man/man2/cachestat.2
> > @@ -0,0 +1,111 @@
> > +.\" 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>
> > +.P
> > +.B struct cachestat_range {
> > +.B "    __u64 off;"
> > +.B "    __u64 len;"
> > +.B };
> > +.P
> > +.B struct cachestat {
> > +.B "    __u64 nr_cache;"
> > +.B "    __u64 nr_dirty;"
> > +.B "    __u64 nr_writeback;"
> > +.B "    __u64 nr_evicted;"
> > +.B "    __u64 nr_recently_evicted;"
> > +.B };
>
> I've wrapped the structures in EX/EE, as is done in other pages.
>
> I've also moved them after the function prototype, to have the function
> stand out more.
>
> > +.P
> > +.BI "int cachestat(unsigned int " fd ", struct cachestat_range *" cstat_range ","
> > +.BI "              struct cachestat *" cstat ", unsigned int " flags ");"
> > +.fi
> > +.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.
> > +.P
> > +The results are returned in a
> > +.B cachestat
> > +structure, pointed to by the
> > +.I cstat
> > +argument.
> > +.P
> > +The
> > +.I .off
> > +and
> > +.I .len
> > +fields must be non-negative.
> > +If
> > +.IR .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.
> > +.P
> > +The
> > +.I flags
> > +argument is reserved for future use and must be set to
> > +.BR 0 .
> > +.
>
> I've removed the line above, since it doesn't do anything.
>
> > +.P
> > +Currently,
> > +.B hugetlbfs
> > +files are not supported.
> > +.SH RETURN VALUE
> > +On success,
> > +.B cachestat()
> > +returns 0.
> > +On error, \-1 is returned,
> > +and
> > +.I errno
> > +is set appropriately.
>
> I've changed this sentence to be consistent with all other pages, which
> say "is set to indicate the error".
>
>
> Have a lovely day!
> Alex
>
> > +.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.
> > +.SH STANDARDS
> > +Linux.
> > +.SH HISTORY
> > +Linux 6.5.
> > +.SH CAVEATS
> > +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.
> > --
> > 2.49.0
> >
> >
>
> --
> <https://www.alejandro-colomar.es/>



-- 
Matteo Croce

perl -e 'for($t=0;;$t++){print chr($t*($t>>8|$t>>13)&255)}' |aplay