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| -rw-r--r-- | Documentation/filesystems/tmpfs.txt | 149 |
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diff --git a/Documentation/filesystems/tmpfs.txt b/Documentation/filesystems/tmpfs.txt deleted file mode 100644 index 5ecbc03e6b2f..000000000000 --- a/Documentation/filesystems/tmpfs.txt +++ /dev/null @@ -1,149 +0,0 @@ -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 will be shown as "Shmem" in /proc/meminfo and "Shared" in -free(1). Notice that these counters also include shared memory -(shmem, see ipcs(1)). The most reliable way to get the count is -using 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_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/admin-guide/cgroup-v1/cpusets.rst] 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/admin-guide/mm/numa_memory_policy.rst 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 -options: - -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. - - -Author: - Christoph Rohland <cr@sap.com>, 1.12.01 -Updated: - Hugh Dickins, 4 June 2007 -Updated: - KOSAKI Motohiro, 16 Mar 2010 |