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Documentation for /proc/sys/fs/*        kernel version 2.2.10

        (c) 1998, 1999,  Rik van Riel 

For general info and legal blurb, please look in README.

==============================================================

This file contains documentation for the sysctl files in

/proc/sys/fs/ and is valid for Linux kernel version 2.2.

The files in this directory can be used to tune and monitor

miscellaneous and general things in the operation of the Linux

kernel. Since some of the files _can_ be used to screw up your

system, it is advisable to read both documentation and source

before actually making adjustments.

Currently, these files are in /proc/sys/fs:

- dentry-state

- dquot-max

- dquot-nr

- file-max

- file-nr

- inode-max

- inode-nr

- inode-state

- overflowuid

- overflowgid

- super-max

- super-nr

Documentation for the files in /proc/sys/fs/binfmt_misc is

in Documentation/binfmt_misc.txt.

==============================================================

dentry-state:

From linux/fs/dentry.c:

--------------------------------------------------------------

struct {

        int nr_dentry;

        int nr_unused;

        int age_limit;         /* age in seconds */

        int want_pages;        /* pages requested by system */

        int dummy[2];

} dentry_stat = {0, 0, 45, 0,};

--------------------------------------------------------------

Dentries are dynamically allocated and deallocated, and

nr_dentry seems to be 0 all the time. Hence it's safe to

assume that only nr_unused, age_limit and want_pages are

used. Nr_unused seems to be exactly what its name says.

Age_limit is the age in seconds after which dcache entries

can be reclaimed when memory is short and want_pages is

nonzero when shrink_dcache_pages() has been called and the

dcache isn't pruned yet.

==============================================================

dquot-max & dquot-nr:

The file dquot-max shows the maximum number of cached disk

quota entries.

The file dquot-nr shows the number of allocated disk quota

entries and the number of free disk quota entries.

If the number of free cached disk quotas is very low and

you have some awesome number of simultaneous system users,

you might want to raise the limit.

==============================================================

file-max & file-nr:

The kernel allocates file handles dynamically, but as yet it

doesn't free them again.

The value in file-max denotes the maximum number of file-

handles that the Linux kernel will allocate. When you get lots

of error messages about running out of file handles, you might

want to increase this limit.

The three values in file-nr denote the number of allocated

file handles, the number of used file handles and the maximum

number of file handles. When the allocated file handles come

close to the maximum, but the number of actually used ones is

far behind, you've encountered a peak in your usage of file

handles and you don't need to increase the maximum.

==============================================================

inode-max, inode-nr & inode-state:

As with file handles, the kernel allocates the inode structures

dynamically, but can't free them yet.

The value in inode-max denotes the maximum number of inode

handlers. This value should be 3-4 times larger than the value

in file-max, since stdin, stdout and network sockets also

need an inode struct to handle them. When you regularly run

out of inodes, you need to increase this value.

The file inode-nr contains the first two items from

inode-state, so we'll skip to that file...

Inode-state contains three actual numbers and four dummies.

The actual numbers are, in order of appearance, nr_inodes,

nr_free_inodes and preshrink.

Nr_inodes stands for the number of inodes the system has

allocated, this can be slightly more than inode-max because

Linux allocates them one pageful at a time.

Nr_free_inodes represents the number of free inodes (?) and

preshrink is nonzero when the nr_inodes > inode-max and the

system needs to prune the inode list instead of allocating

more.

==============================================================

overflowgid & overflowuid:

Some filesystems only support 16-bit UIDs and GIDs, although in Linux

UIDs and GIDs are 32 bits. When one of these filesystems is mounted

with writes enabled, any UID or GID that would exceed 65535 is translated

to a fixed value before being written to disk.

These sysctls allow you to change the value of the fixed UID and GID.

The default is 65534.

==============================================================

super-max & super-nr:

These numbers control the maximum number of superblocks, and

thus the maximum number of mounted filesystems the kernel

can have. You only need to increase super-max if you need to

mount more filesystems than the current value in super-max

allows you to.