Subject: Re: Swap overcommit (was Re: Replacement for grep(1) (part 2))
To: Noriyuki Soda <>
From: Matthew Dillon <>
List: tech-userlevel
Date: 07/15/1999 11:25:39
::    -s             Print summary information  about  total  swap
::                   space usage and availability:
::                      allocated   The total amount of swap space
::                                  (in      1024-byte     blocks)
::                                  currently allocated for use as
::                                  backing store.
::                      reserved    The total amount of swap space
::                                  (in   1024-bytes  blocks)  not
::                                  currently    allocated,    but
::                                  claimed by memory mappings for
::                                  possible future use.
::                      used        The total amount of swap space
::                                  (in  1024-byte blocks) that is
::                                  either allocated or reserved.

    It would be really easy to test this.

    Write a program that malloc's 32MB of space and touches it,
    then sleeps 10 seconds and forks, with both child and parent
    sleeping afterwords.  ( the parent and the forked child should
    not touch the memory after the fork occurs ).

    Do a pstat -s before, after the initial touch, and after
    the fork.  If you do not see the reserved swap space jump
    by 32MB after the fork, it isn't what you thought it was.

					Matthew Dillon