NAME¶
/etc/cachefilesd.conf - Local file caching configuration file
SYNOPSIS¶
The configuration file for cachefilesd which can manage a persistent cache for a
variety of network filesystems using a set of files on an already mounted
filesystem as the data store.
DESCRIPTION¶
This configuration file can contain a number of commands. Each one should be on
a separate line. Blank lines and lines beginning with a '#' character are
considered to be comments and are discarded.
The only mandatory command is:
- dir <path>
- This command specifies the directory containing the root of
the cache. It may only specified once per configuration file.
All the other commands are optional:
- brun <N>%
- bcull <N>%
- bstop <N>%
- frun <N>%
- fcull <N>%
- fstop <N>%
- These commands configure the culling limits. The defaults
are 7% (run), 5% (cull) and 1% (stop) respectively. See the section on
cache culling for more information.
- The commands beginning with a 'b' are file space (block)
limits, those beginning with an 'f' are file count limits.
- tag <name>
- This command specifies a tag to FS-Cache to use in
distinguishing multiple caches. This is only required if more than one
cache is going to be used. The default is "CacheFiles".
- culltable <log2size>
- This command specifies the size of the tables holding the
lists of cullable objects in the cache. The bigger the number, the faster
and more smoothly that culling can proceed when there are many objects in
the cache, but the more memory will be consumed by cachefilesd.
- The quantity is specified as log2 of the size actually
required, for example 12 indicates a table of 4096 entries and 13
indicates 8192 entries. The permissible values are between 12 and 20, the
latter indicating 1048576 entries. The default is 12.
- debug <mask>
- This command specifies a numeric bitmask to control
debugging in the kernel module. The default is zero (all off). The
following values can be OR'd into the mask to collect various
information:
- 1
- Turn on trace of function entry (_enter() macros)
- 2
- Turn on trace of function exit (_leave() macros)
- 4
- Turn on trace of internal debug points (_debug())
- This mask can also be set through
/sys/module/cachefiles/parameters/debug.
EXAMPLES¶
As an example, consider the following:
dir /var/fscache
tag mycache
brun 10%
bcull 7%
bstop 3%
The places the cache storage objects in a directory called
"/var/fscache", names the cache "mycache", permits the
cache to run freely as long as there's at least 10% free space on
/var/fscache/, starts culling the cache when the free space drops below 7% and
stops writing new stuff into the cache if the amount of free space drops below
3%. If the cache is suspended, it won't reactivate until the amount of free
space rises again to 10% or better.
CACHE CULLING¶
The cache may need culling occasionally to make space. This involves discarding
objects from the cache that have been used less recently than anything else.
Culling is based on the access time of data objects. Empty directories are
culled if not in use.
Cache culling is done on the basis of the percentage of blocks and the
percentage of files available in the underlying filesystem. There are six
"limits":
- brun
- frun
- If the amount of free space and the number of available
files in the cache rises above both these limits, then culling is turned
off.
- bcull
- fcull
- If the amount of available space or the number of available
files in the cache falls below either of these limits, then culling is
started.
- bstop
- fstop
- If the amount of available space or the number of available
files in the cache falls below either of these limits, then no further
allocation of disk space or files is permitted until culling has raised
things above these limits again.
These must be configured thusly:
- 0 <= bstop < bcull < brun < 100
0 <= fstop < fcull < frun < 100
Note that these are percentages of available space and available files, and do
not appear as 100 minus the percentage displayed by the
df
program.
The userspace daemon scans the cache to build up a table of cullable objects.
These are then culled in least recently used order. A new scan of the cache is
started as soon as space is made in the table. Objects will be skipped if
their atimes have changed or if the kernel module says it is still using them.
SEE ALSO¶
cachefilesd(8),
df(1), /usr/share/doc/cachefilesd-*/README
AUTHORS¶
The cachefilesd software has been developed by David Howells
