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Diffstat (limited to 'disk-utils/mkswap.8')
| -rw-r--r-- | disk-utils/mkswap.8 | 56 |
1 files changed, 38 insertions, 18 deletions
diff --git a/disk-utils/mkswap.8 b/disk-utils/mkswap.8 index 2c02fbbe0..643d7ba04 100644 --- a/disk-utils/mkswap.8 +++ b/disk-utils/mkswap.8 @@ -7,13 +7,13 @@ .\" " .TH MKSWAP 8 "8 February 1995" "Linux 1.0" "Linux Programmer's Manual" .SH NAME -mkswap \- set up a Linux swap device +mkswap \- set up a Linux swap area .SH SYNOPSIS .B "mkswap [ \-c ]" .IB device " [" size-in-blocks "]" .SH DESCRIPTION .B mkswap -sets up a Linux swap area on a device (usually a disk partition). +sets up a Linux swap area on a device or in a file. The .I device @@ -31,23 +31,45 @@ is usually of the following form: The .I size-in-blocks parameter is the desired size of the file system, in blocks. This -information is determined automatically by mkswap if it is omitted. Block -counts are rounded down to pages of 4 kB each. Only block counts equal to -or greater than 40 and equal to or less than 131072 are allowed. Block -counts greater than 130752 are (silently) rounded down to 130752. +information is determined automatically by +.B mkswap +if it is omitted. Block counts are rounded down so that the total +size is an integer multiple of the machine's page size. Only block +counts in the range MINCOUNT..MAXCOUNT are allowed. If the block count +exceeds the MAXCOUNT, it is truncated to that value and a warning +message is issued. + +The MINCOUNT and MAXCOUNT values for a swap area are: -As Nick Holloway explains, the actual maximum for each swap file/partition -is: .RS -(4096 - 10) * 8 * 4096 = 133890048 bytes = 130752 blocks = 127.6875 Mb +MINCOUNT = 10 * PAGE_SIZE / 1024 +.br +MAXCOUNT = (PAGE_SIZE - 10) * 8 * PAGE_SIZE / 1024 .RE -This is because a single page is used to hold the swap bitmap at the -start of the partition, where each bit is a single 4K page. The reason -for the -10, is that the signature is "SWAP-SPACE" -- 10 characters. -.B mkswap -can also set up swap files, although the file has to be created first. A -sequence of commands similar to the following is reasonable for this +For example, on a machine with 4kB pages (e.g., x86), we get: + +.RS +MINCOUNT = 10 * 4096 / 1024 = 40 +.br +MAXCOUNT = (4096 - 10) * 8 * 4096 / 1024 = 130752 +.RE + +As each block is 1kB large, the swap area in this example could have a +size that is anywhere in the range from 40kB up to 127.6875MB. + +If you don't know the page size that your machine uses, you may be +able to look it up with "cat /proc/cpuinfo". + +The reason for the limit on MAXCOUNT is that a single page is used to +hold the swap bitmap at the start of the swap area, where each bit +represents a single page. The reason for the -10, is that the +signature is "SWAP-SPACE" -- 10 characters. + +To setup a swap file, it is necessary to create that file before +running +.B mkswap . +A sequence of commands similar to the following is reasonable for this purpose: .nf @@ -59,9 +81,7 @@ purpose: .RE .fi -Note that the regular file has to be created before running -.B mkswap -on the file, and that the file must not contain any holes (so, using +Note that a swap file must not contain any holes (so, using .BR cp (1) to create the file is not acceptable). |