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/Documentation/sysctl/fs.txt

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  1Documentation for /proc/sys/fs/*	kernel version 2.2.10
  2	(c) 1998, 1999,  Rik van Riel <riel@nl.linux.org>
  3
  4For general info and legal blurb, please look in README.
  5
  6==============================================================
  7
  8This file contains documentation for the sysctl files in
  9/proc/sys/fs/ and is valid for Linux kernel version 2.2.
 10
 11The files in this directory can be used to tune and monitor
 12miscellaneous and general things in the operation of the Linux
 13kernel. Since some of the files _can_ be used to screw up your
 14system, it is advisable to read both documentation and source
 15before actually making adjustments.
 16
 17Currently, these files are in /proc/sys/fs:
 18- dentry-state
 19- dquot-max
 20- dquot-nr
 21- file-max
 22- file-nr
 23- inode-max
 24- inode-nr
 25- inode-state
 26- overflowuid
 27- overflowgid
 28- super-max
 29- super-nr
 30
 31Documentation for the files in /proc/sys/fs/binfmt_misc is
 32in Documentation/binfmt_misc.txt.
 33
 34==============================================================
 35
 36dentry-state:
 37
 38From linux/fs/dentry.c:
 39--------------------------------------------------------------
 40struct {
 41        int nr_dentry;
 42        int nr_unused;
 43        int age_limit;         /* age in seconds */
 44        int want_pages;        /* pages requested by system */
 45        int dummy[2];
 46} dentry_stat = {0, 0, 45, 0,};
 47-------------------------------------------------------------- 
 48
 49Dentries are dynamically allocated and deallocated, and
 50nr_dentry seems to be 0 all the time. Hence it's safe to
 51assume that only nr_unused, age_limit and want_pages are
 52used. Nr_unused seems to be exactly what its name says.
 53Age_limit is the age in seconds after which dcache entries
 54can be reclaimed when memory is short and want_pages is
 55nonzero when shrink_dcache_pages() has been called and the
 56dcache isn't pruned yet.
 57
 58==============================================================
 59
 60dquot-max & dquot-nr:
 61
 62The file dquot-max shows the maximum number of cached disk
 63quota entries.
 64
 65The file dquot-nr shows the number of allocated disk quota
 66entries and the number of free disk quota entries.
 67
 68If the number of free cached disk quotas is very low and
 69you have some awesome number of simultaneous system users,
 70you might want to raise the limit.
 71
 72==============================================================
 73
 74file-max & file-nr:
 75
 76The kernel allocates file handles dynamically, but as yet it
 77doesn't free them again.
 78
 79The value in file-max denotes the maximum number of file-
 80handles that the Linux kernel will allocate. When you get lots
 81of error messages about running out of file handles, you might
 82want to increase this limit.
 83
 84The three values in file-nr denote the number of allocated
 85file handles, the number of unused file handles and the maximum
 86number of file handles. When the allocated file handles come
 87close to the maximum, but the number of unused file handles is
 88significantly greater than 0, you've encountered a peak in your 
 89usage of file handles and you don't need to increase the maximum.
 90
 91==============================================================
 92
 93inode-max, inode-nr & inode-state:
 94
 95As with file handles, the kernel allocates the inode structures
 96dynamically, but can't free them yet.
 97
 98The value in inode-max denotes the maximum number of inode
 99handlers. This value should be 3-4 times larger than the value
100in file-max, since stdin, stdout and network sockets also
101need an inode struct to handle them. When you regularly run
102out of inodes, you need to increase this value.
103
104The file inode-nr contains the first two items from
105inode-state, so we'll skip to that file...
106
107Inode-state contains three actual numbers and four dummies.
108The actual numbers are, in order of appearance, nr_inodes,
109nr_free_inodes and preshrink.
110
111Nr_inodes stands for the number of inodes the system has
112allocated, this can be slightly more than inode-max because
113Linux allocates them one pageful at a time.
114
115Nr_free_inodes represents the number of free inodes (?) and
116preshrink is nonzero when the nr_inodes > inode-max and the
117system needs to prune the inode list instead of allocating
118more.
119
120==============================================================
121
122overflowgid & overflowuid:
123
124Some filesystems only support 16-bit UIDs and GIDs, although in Linux
125UIDs and GIDs are 32 bits. When one of these filesystems is mounted
126with writes enabled, any UID or GID that would exceed 65535 is translated
127to a fixed value before being written to disk.
128
129These sysctls allow you to change the value of the fixed UID and GID.
130The default is 65534.
131
132==============================================================
133
134super-max & super-nr:
135
136These numbers control the maximum number of superblocks, and
137thus the maximum number of mounted filesystems the kernel
138can have. You only need to increase super-max if you need to
139mount more filesystems than the current value in super-max
140allows you to.
141
142==============================================================
143
144aio-nr & aio-max-nr:
145
146aio-nr shows the current system-wide number of asynchronous io
147requests.  aio-max-nr allows you to change the maximum value
148aio-nr can grow to.
149
150==============================================================