cachefilesd.conf(5)
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:
secctx <label>
Specify an LSM security context as which the kernel will perform
operations to access the cache. The default is to use
cachefilesd's security context. Files will be created in the
cache with the label of directory specified to the 'dir'
command.
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.
nocull Disable culling. Culling and building up the cull table take up
a certain amount of a systems resources, which may be
undesirable. Supplying this option disables all culling
activity. The cache will keep building up to the limits set and
won't be shrunk, except by the removal of out-dated cache files.
resume_thresholds <blocks> <files>
This command specifies the amount of blocks or files that the
kernel should let go of before the daemon should resume from
culling table scan suspension.
Scanning to refill the cull table is suspended when all the
objects in a cache are pinned by a live network filesystem in
the kernel and there's nothing to cull.
Either value can be "-" to indicate that this threshold should
be ignored.
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/cache/fscache
secctx cachefiles_kernel_t
tag mycache
brun 10%
bcull 7%
bstop 3%
secctx system_u:system_r:cachefiles_kernel_t:s0
This places the cache storage objects in a directory called
"/var/cache/fscache", names the cache "mycache", permits the cache to
run freely as long as there's at least 10% free space on
/var/cache/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.
Furthermore, this will tell the kernel module the security context it
should use when accessing the cache (SELinux is assumed to be the LSM
in this example). In this case, SELinux would use cachefiles_kernel_t
as the key into the policy.
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.
Culling can be disabled with the nocull option.
SEE ALSO
cachefilesd(8), df(1), /usr/share/doc/cachefilesd/README
AUTHORS
David Howells <dhowells@redhat.com>
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