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+Tmpfs is a file system which keeps all files in virtual memory.
+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 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 ...'
+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.
+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 has the following uses:
+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.
+ 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.
+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:
+ tmpfs /dev/shm tmpfs defaults 0 0
+ Remember to create the directory that you intend to mount tmpfs on
+ if necessary.
+ 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)
+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.
+4) And probably a lot more I do not know about :-)
+tmpfs has three mount options for sizing:
+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
+ machine with highmem) the number of lowmem RAM pages,
+ whichever is the lower.
+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%
+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.
+tmpfs has a mount option to set the NUMA memory allocation policy for
+all files in that instance (if CONFIG_NUMA is enabled) - which can be
+adjusted on the fly via 'mount -o remount ...'
+mpol=default use the process allocation policy
+ (see set_mempolicy(2))
+mpol=prefer:Node prefers to allocate memory from the given Node
+mpol=bind:NodeList allocates memory only from nodes in NodeList
+mpol=interleave prefers to allocate from each node in turn
+mpol=interleave:NodeList allocates from each node of NodeList in turn
+mpol=local prefers to allocate memory from the local node
+NodeList format is a comma-separated list of decimal numbers and ranges,
+a range being two hyphen-separated decimal numbers, the smallest and
+largest node numbers in the range. For example, mpol=bind:0-3,5,7,9-15
+A memory policy with a valid NodeList will be saved, as specified, for
+use at file creation time. When a task allocates a file in the file
+system, the mount option memory policy will be applied with a NodeList,
+if any, modified by the calling task's cpuset constraints
+[See Documentation/cgroups/cpusets.txt] and any optional flags, listed
+below. If the resulting NodeLists is the empty set, the effective memory
+policy for the file will revert to "default" policy.
+NUMA memory allocation policies have optional flags that can be used in
+conjunction with their modes. These optional flags can be specified
+when tmpfs is mounted by appending them to the mode before the NodeList.
+See Documentation/vm/numa_memory_policy.txt for a list of all available
+memory allocation policy mode flags and their effect on memory policy.
+ =static is equivalent to MPOL_F_STATIC_NODES
+ =relative is equivalent to MPOL_F_RELATIVE_NODES
+For example, mpol=bind=static:NodeList, is the equivalent of an
+allocation policy of MPOL_BIND | MPOL_F_STATIC_NODES.
+Note that trying to mount a tmpfs with an mpol option will fail if the
+running kernel does not support NUMA; and will fail if its nodelist
+specifies a node which is not online. If your system relies on that
+tmpfs being mounted, but from time to time runs a kernel built without
+NUMA capability (perhaps a safe recovery kernel), or with fewer nodes
+online, then it is advisable to omit the mpol option from automatic
+mount options. It can be added later, when the tmpfs is already mounted
+on MountPoint, by 'mount -o remount,mpol=Policy:NodeList MountPoint'.
+To specify the initial root directory you can use the following mount
+mode: The permissions as an octal number
+uid: The user id
+gid: The group 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.
+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.
+ Christoph Rohland <cr@sap.com>, 1.12.01
+ Hugh Dickins, 4 June 2007
+ KOSAKI Motohiro, 16 Mar 2010