2 .\" Copyright (c) 2007 Xin LI
3 .\" Copyright (c) 2017 The FreeBSD Foundation, Inc.
5 .\" Part of this documentation was written by
6 .\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship
7 .\" from the FreeBSD Foundation.
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61 .Nd "in-memory file system"
63 To compile this driver into the kernel,
64 place the following line in your
65 kernel configuration file:
66 .Bd -ragged -offset indent
70 Alternatively, to load the driver as a
71 module at boot time, place the following line in
73 .Bd -literal -offset indent
79 driver implements an in-memory, or
82 The filesystem stores both file metadata and data in main memory.
83 This allows very fast and low latency accesses to the data.
85 An umount or system reboot invalidates it.
86 These properties make the filesystem's mounts suitable for fast
90 If the system becomes low on memory and swap is configured (see
92 the system can transfer file data to swap space, freeing memory
94 Metadata, including the directory content, is never swapped out by the
95 current implementation.
96 Keep this in mind when planning the mount limits, especially when expecting
97 to place many small files on a tmpfs mount.
101 is used on a file from a tmpfs mount, the swap VM object managing the
102 file pages is used to implement mapping and avoid double-copying of
104 This quirk causes process inspection tools, like
106 to report anonymous memory mappings instead of file mappings.
108 The following options are available when
112 .Bl -tag -width "It Cm maxfilesize"
114 Specifies the group ID of the root inode of the file system.
115 Defaults to the mount point's GID.
117 Specifies the user ID of the root inode of the file system.
118 Defaults to the mount point's UID.
120 Specifies the mode (in octal notation) of the root inode of the file system.
121 Defaults to the mount point's mode.
123 Do not use namecache to resolve names to files for the created mount.
124 This saves memory, but currently might impair scalability for highly
125 used mounts on large machines.
127 Specifies the maximum number of nodes available to the file system.
128 If not specified, the file system chooses a reasonable maximum based on
129 the file system size, which can be limited with the
133 Specifies the total file system size in bytes, unless suffixed
134 with one of k, m, g, t, or p, which denote byte, kilobyte,
135 megabyte, gigabyte, terabyte and petabyte respectively.
136 If zero (the default) or a value larger than SIZE_MAX - PAGE_SIZE
137 is given, the available amount of memory (including
138 main memory and swap space) will be used.
140 Specifies the maximum file size in bytes.
141 Defaults to the maximum possible value.
148 .Dl "mount -t tmpfs tmpfs /tmp"
162 driver first appeared in
168 kernel implementation was written by
169 .An Julio M. Merino Vidal Aq Mt jmmv@NetBSD.org
170 as a Google Summer of Code project.
173 and others ported it from
178 This manual page was written by
179 .An Xin LI Aq Mt delphij@FreeBSD.org .