==================================
ϡ
linux-2.6.13-rc3/Documentation/filesystems/tmpfs.txt 
Ǥ
Ρ JF ץ < http://www.linux.or.jp/JF/ >
  2005/7/25
  Hiroshi.Suzuki < setter at reset dot jp >
  Chie Nakatani  <jeanne at mbox dot kyoto-inet dot or dot jp>
==================================

Tmpfs is a file system which keeps all files in virtual memory.

Tmpfs ϡۥեݻե륷ƥǤ

Everything in tmpfs is temporary in the sense that no files will be
created on your hard drive. If you unmount a tmpfs instance,
everything stored therein is lost.

tmpfs  ƤϰŪʤΤǡϡɥǥˤϥեϺޤ
tmpfs ޥȲС¸줿٤ƤΤΤϼʤޤ

tmpfs puts everything into the kernel internal caches and grows and
shrinks to accommodate the files it contains and is able to swap
unneeded pages out to swap space. It has maximum size limits which can
be adjusted on the fly via 'mount -o remount ...'

tmpfs ϡƤ򥫡ͥå֤ޤޤեˤ碌
礭⾮ʤꡢפʥڡϥåץȤޤ
ˤϡ祵¤ޤ'mount -o remount ...' ǡĴǽǤ

If you compare it to ramfs (which was the template to create tmpfs)
you gain swapping and limit checking. Another similar thing is the RAM
disk (/dev/ram*), which simulates a fixed size hard disk in physical
RAM, where you have to create an ordinary filesystem on top. Ramdisks
cannot swap and you do not have the possibility to resize them. 

(tmpfs ƥץ졼ȤǤä) ramfs Ӥȡåפȡ¥åޤ
⤦ҤȤ̤ɤΤϡRAM ǥ( /dev/ram ) ǡʪRAM ˥
ꤷϡɥǥ򡢥ߥ졼ȤޤǾ̤ˡ̾Υե륷ƥ
ʤФʤޤRAM ǥϥåפǤޤ󤷡ѹǤޤ

Since tmpfs lives completely in the page cache and on swap, all tmpfs
pages currently in memory will show up as cached. It will not show up
as shared or something like that. Further on you can check the actual
RAM+swap use of a tmpfs instance with df(1) and du(1).

tmpfs ϡʷǥڡåȥåפ˾ˤΤǡ
Ƥ tmpfs ڡϡå夵줿ΤȤƸǤ礦
ϡͭ줿(ޤΤ)ȤƤϸޤ
ˡtmpfs ˤѤƤ RAM+swap ϡdf(1)du(1) ǡĴ٤뤳ȤǤޤ

tmpfs has the following uses:

tmpfs ϡʲӤäƤޤ

1) There is always a kernel internal mount which you will not see at
   all. This is used for shared anonymous mappings and SYSV shared
   memory. 

1) 뤳ȤΤǤʤͥޥȤ¸ߤޤ
   ϡƿ̾ζͭޥåԥ󥰤䡢SYSV ͭ˻Ѥޤ

   This mount does not depend on CONFIG_TMPFS. If CONFIG_TMPFS is not
   set, the user visible part of tmpfs is not build. But the internal
   mechanisms are always present.

   ΥޥȤCONFIG_TMPFS˰¸ޤ
   CONFIG_TMPFS åȤʤ硢tmpfs  Υ桼ĻȤ߹ޤޤ
   ᥫ˥ϡ¸ߤޤ

2) glibc 2.2 and above expects tmpfs to be mounted at /dev/shm for
   POSIX shared memory (shm_open, shm_unlink). Adding the following
   line to /etc/fstab should take care of this:

2) glibc 2.2 ʹߤξ硢tmpfs ϡPOSIX ͭ(shm_openshm_unlink) Τˡ
    /dev/shm ˥ޥȤʤФޤ
    /etc/fstab ˡʲιԤɲäȤդƤ

	tmpfs	/dev/shm	tmpfs	defaults	0 0

   Remember to create the directory that you intend to mount tmpfs on
   if necessary (/dev/shm is automagically created if you use devfs).

   tmpfs ޥȤͽ꤬硢ΤΥǥ쥯ȥ뤳Ȥ˺ʤǤ
   ( /dev/shm ϡdevfs Ȥʤ鼫ưŪ˺ޤ)

   This mount is _not_ needed for SYSV shared memory. The internal
   mount is used for that. (In the 2.3 kernel versions it was
   necessary to mount the predecessor of tmpfs (shm fs) to use SYSV
   shared memory)

   ΥޥȤϡSYSV ͭˤ *ɬפޤ*
   ޥȤѤޤ( С2.3ϥͥǤϡSYSV ͭ Ȥˡ
   tmpfs (shm fs) ȤȤơޥȤ򤹤ɬפޤ )

3) Some people (including me) find it very convenient to mount it
   e.g. on /tmp and /var/tmp and have a big swap partition. And now
   loop mounts of tmpfs files do work, so mkinitrd shipped by most
   distributions should succeed with a tmpfs /tmp.

3) /tmp  /var/tmp礭ʥåץѡƥäƤ硢
   ޥȤΤϤȤƤȹͤͤ⤤ޤʻ⤽Ǥˡ
   ޤߡtmpfs ե ƵŪޥȤȤޤǤ顢¿Υǥȥӥ塼
   ˴ޤޤ mkinitrd ϡtmpfs /tmp ǤưϤǤ

4) And probably a lot more I do not know about :-)

4) ֤󡢻Τ狼ʤȤäȤ󤢤ϤǤ :-)

tmpfs has three mount options for sizing:

tmpfs ˤϥꤹ뤿3ĤΥޥȥץ󤬤ޤ

size:      The limit of allocated bytes for this tmpfs instance. The 
           default is half of your physical RAM without swap. If you
           oversize your tmpfs instances the machine will deadlock
           since the OOM handler will not be able to free that memory.
nr_blocks: The same as size, but in blocks of PAGE_CACHE_SIZE.
nr_inodes: The maximum number of inodes for this instance. The default
           is half of the number of your physical RAM pages, or (on a
           a machine with highmem) the number of lowmem RAM pages,
           whichever is the lower.

size:	      tmpfs ФƳƤХȿξ¡
          ǥեȤϡåפʪȾʬtmpfs 󥹥󥹤³Ķ
          礭ˤȡOOM ϥɥ餬Ǥޥ󤬥ǥåɥå뤫⤷ޤ
nr_brocks: size ƱǤPAGE_CACHE_SIZE Υ֥åꤷޤ
nr_inodes: Υ󥹥󥹤 inode ǥեȤϡʪ RAM ڡȾʬޤϡ
          (highmem ޥ) lowmem RAM ڡ Τɤ餫

These parameters accept a suffix k, m or g for kilo, mega and giga and
can be changed on remount.  The size parameter also accepts a suffix %
to limit this tmpfs instance to that percentage of your physical RAM:
the default, when neither size nor nr_blocks is specified, is size=50%

ѥ᡼ϡkmg(줾졢ᥬ) 򥵥եåǤ
ƥޥȻѹǤޤsize ѥ᡼ϡʪRAMΤФ 
tmpfs 󥹥󥹤ξ¥ˤ뤿ˡ% Ȥޤsizenr_brocks 
ɤꤷʤΥǥեȤϡsize=50% Ǥ 

If nr_blocks=0 (or size=0), blocks will not be limited in that instance;
if nr_inodes=0, inodes will not be limited.  It is generally unwise to
mount with such options, since it allows any user with write access to
use up all the memory on the machine; but enhances the scalability of
that instance in a system with many cpus making intensive use of it.

nr_blocks=0 ( ޤϡsize=0 ) ξ硢Υ󥹥󥹤Ǥϡblock ̵¤ˤʤޤ
nr_inode=0 ξ硢inode ̵¤ǤŪˤ饪ץȤäƥޥȤ뤳Ȥϡ
򤫤ʤȤǤ߸ĥ桼ޥΥȤ̤ƤޤǤ
Ū˻Ѥ롢 CPU ĥƥǡΥ󥹥󥹤
ӥƥޤ

To specify the initial root directory you can use the following mount
options:

롼ȥǥ쥯ȥꤹ뤿ᡢΥޥȥץ󤬻Ȥޤ

mode:	The permissions as an octal number
uid:	The user id 
gid:	The group id

mode:      8ʿˤ°Υ⡼
uid: 桼 ID
gid: 롼 ID

These options do not have any effect on remount. You can change these
parameters with chmod(1), chown(1) and chgrp(1) on a mounted filesystem.

饪ץϡƥޥȻϤޤ
ѥ᡼ϡޥȤ줿ե륷ƥǡchmod(1), chown(1), chgrp(1) 
ˤäѹǤޤ


So 'mount -t tmpfs -o size=10G,nr_inodes=10k,mode=700 tmpfs /mytmpfs'
will give you tmpfs instance on /mytmpfs which can allocate 10GB
RAM/SWAP in 10240 inodes and it is only accessible by root.

äơ 'mount -t tmpfs -o size=10G,nr_inodes=10k,mode=700 tmpfs /mytmpfs'
Ǥϡ /mytmpfs  tmpfs 󥹥󥹤ǡ10240ʲ inode  RAM/SWAP  
10GB ƤǤޤroot Ǥޤ

Author:
   Christoph Rohland <cr at sap dot com>, 1.12.01
Updated:
   Hugh Dickins <hugh at veritas dot com>, 13 March 2005
