Date: Thu, 26 Jan 2017 11:07:36 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r312811 - stable/10/share/man/man5 Message-ID: <201701261107.v0QB7aQO054823@repo.freebsd.org>
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Author: kib Date: Thu Jan 26 11:07:36 2017 New Revision: 312811 URL: https://svnweb.freebsd.org/changeset/base/312811 Log: MFC r312423: Refresh tmpfs(5) man page. MFC r312648: Editing and clarifications for tmpfs(5). Modified: stable/10/share/man/man5/tmpfs.5 Directory Properties: stable/10/ (props changed) Modified: stable/10/share/man/man5/tmpfs.5 ============================================================================== --- stable/10/share/man/man5/tmpfs.5 Thu Jan 26 11:06:39 2017 (r312810) +++ stable/10/share/man/man5/tmpfs.5 Thu Jan 26 11:07:36 2017 (r312811) @@ -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 an 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, like +.Pa /tmp . +.Pp +If the system becomes low on memory and swap is configured (see +.Xr swapon 8 ), +the system can transfer file data to swap space, freeing memory +for other needs. +Metadata, including the directory content, is never swapped out by the +current implementation. +Keep this in mind when planning the mount limits, especially when expecting +to place many small files on a tmpfs mount. +.Pp +When +.Xr mmap 2 +is used on a file from a tmpfs mount, the swap VM object managing the +file pages is used to implement mapping and 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 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 delphij@FreeBSD.org . -.Sh BUGS -Some file system mount time options may not be well-supported.
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