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fadvise

NAME

fadvise - File ADVISE: give file advisory information

SYNOPSIS

fadvise [options] file [...]

  Options:
   -help - brief help message
   -man - full documentation
   -sequential
   -random
   -willneed
   -dontneed
   -noreuse
   -normal (default)
   -offset=n
   -length=n
   -verbose
   -noverbose
 
 

OPTIONS

-help

Shows usage information and exits.

-man

Shows the manual page and exits.

-offset=n

Specifies offset for fadvise. Defaults to zero if unspecified.

-length=n

Specifies length for fadvise. Defaults to zero if unspecified, i.e. the whole file if offset is also zero.

-verbose

Shows incore page info after fadvise.

-noverbose

Doesn't show incore page info after fadvise. This is the default.

-sequential

Announces the expectation to access the file sequentially.

-random

Announces the expectation to access the file randomly.

-willneed

Announces the expectation that file content will be needed in the near future.

-dontneed

Announces the expectation that file content won't be needed in the near future.

Under Linux 2.6.9, this is known to cause the file content to be evicted from the buffer-cache immediately.

Note that this option first causes an fsync of the file.

-noreuse

Announces the expectation that file content won't be reused in the near future.

-normal

Announces the expectation to access the file normally. This is the default.

DESCRIPTION

fadvise is a command used to give file advisory information to the operating system.

Its ``don't need'' option (fadvise --dontneed) is particularly useful to cause the files' pages (blocks) to be evicted from the buffer-cache.

EXAMPLE

  $ fadvise --verbose --dontneed foo.rrd
  page size: 4096
  foo.rrd: no incore pages.
 
 

BUGS

-dontneed might be the only really useful option.

In verbose mode, you may get an error from mincore such as ``cannot allocate memory'' if the file size is zero.

Some operating systems have posix_fadvise, but it doesn't work. For instance under Linux 2.4, you may see this error:

  posix_fadvise: Inappropriate ioctl for device
 
 

AUTHOR

Dave Plonka <plonka@cs.wisc.edu>

Copyright (C) 2007 Dave Plonka. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

VERSION

This is fadvise $Revision: 1.5 $.

SEE ALSO

The fincore command.