d/freebsd-skq
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Refresh tmpfs(5) man page.

Browse Source 
Provide more useful explanation of features and quirks.

Reviewed by:	emaste, vangyzen
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D9211
This commit is contained in:
Konstantin Belousov 2017-01-19 18:26:06 +00:00
parent 0195177b26
commit 3ee2462017
1 changed files with 41 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

52
share/man/man5/tmpfs.5
View File

@ -1,7 +1,12 @@
.\"-
.\" Copyright (c) 2007 Xin LI
.\" Copyright (c) 2017 The FreeBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" Part of this documentation was written by
.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship
.\" from the FreeBSD Foundation.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
@ -49,12 +54,12 @@
.\"
.\" $FreeBSD$
.\"
.Dd April 23, 2012
.Dd January 17, 2017
.Dt TMPFS 5
.Os
.Sh NAME
.Nm tmpfs
.Nd "efficient memory file system"
.Nd "in-memory file system"
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
@ -72,17 +77,40 @@ tmpfs_load="YES"
.Sh DESCRIPTION
The
.Nm
driver will permit the
.Fx
kernel to access
driver implements in-memory, or
.Tn tmpfs
file systems.
file system.
The filesystem stores both file metadata and data in main memory.
This allows very fast and low latency accesses to the data.
The data is volatile.
An umount or system reboot invalidates it.
These properties make the filesystem's mounts suitable for fast
scratch storage, e.g.
.Pa /tmp .
.Pp
If the system becomes low on memory and swap is configured (see
.Xr swapon 8 ),
file data may be written to the swap space, freeing memory
for other needs.
The current implementation never swaps out metadata, including
the directory content.
Keep this in mind when planning the mount limits, especially when expecting
to place many small files on a tmpfs mount.
.Pp
When a file from a tmpfs mount is mmaped (see
.Xr mmap 2 )
into the process address space, the swap VM object which manages the file
pages is used to implement mapping and to avoid double-copying of
the file data.
This quirk causes process inspection tools, like
.Xr procstat 1 ,
to report anonymous memory mappings instead of file mappings.
.Sh OPTIONS
The following options are available when
mounting
.Nm
file systems:
.Bl -tag -width indent
.Bl -tag -width "It Cm maxfilesize"
.It Cm gid
Specifies the group ID of the root inode of the file system.
Defaults to the mount point's GID.
@ -114,11 +142,15 @@ memory file system:
.Pp
.Dl "mount -t tmpfs tmpfs /tmp"
.Sh SEE ALSO
.Xr procstat 1 ,
.Xr nmount 2 ,
.Xr mmap 2 ,
.Xr unmount 2 ,
.Xr fstab 5 ,
.Xr mdmfs 8 ,
.Xr mount 8
.Xr mount 8 ,
.Xr swapinfo 8 ,
.Xr swapon 8
.Sh HISTORY
The
.Nm
@ -130,7 +162,7 @@ The
.Nm
kernel implementation was written by
.An Julio M. Merino Vidal Aq Mt jmmv@NetBSD.org
as a Google SoC project.
as a Google Summer of Code project.
.Pp
.An Rohit Jalan
and others ported it from
@ -140,5 +172,3 @@ to
.Pp
This manual page was written by
.An Xin LI Aq Mt delphij@FreeBSD.org .
.Sh BUGS
Some file system mount time options may not be well-supported.