Path: utzoo!dciem!nrcaer!julie!mcr
From: mcr@julie.UUCP (Michael Richardson)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Virtual Memory / doable 1.4 request
Message-ID: <1312.AA1312@julie>
Date: 21 May 89 23:45:28 GMT
References: <8905132040.AA27524@postgres.Berkeley.EDU>
Followup-To: comp.sys.amiga.tech
Organization: Sandleman Software Works' Debugging Department, Ottawa, ON
Lines: 43

>            (B) Open(file,1006) and write nothing yet.  Assume you will be
>                able to extend the file as needed to 20MB, map 20MB worth of

>                * my favorite, medium difficulty.  One would eventually want
>                  to add a ftruncate() command to the filesystem to do this
>                  right though.

  Mine too. However, going through the file system isn't the hottest
idea ever invented. The blocks that the file occupies (and we are
talking FFS here) would be placed in a table, and raw accesses to the
disk could be made. This would, however, be an optimisation.
There is no reason to reinvent the network disk (nd) and then get rid of
it again.
  Masscomp RTU essentially does this by using a special file type
called a "contiguous" file. (Because the blocks are all contiguous, i.e.
in a row) [This type is there for dumping high speed incoming data
to]

>                File fragmentation is not a problem.. the user can put the
>                file on a little-used or unused partition, or make a partition
>                specifically to hold the VM-file (but it is his choice!).
  But the size of the swap is still limited by the size of the partition.
If the partition is unused, better to go direct, and how many users have
"little-used" partitions that are not either 98.7% full, read-only
or both... Still, user's choice is good.

>                The one advantage is that on system crash the OS can raw-write
>                VM to the swap partition without worrying about destroying
>                files (cause there are none).  Using a file for VM means that
>                on system crash you cannot dump core.  I don't we want to loose
>                the functionality of files for paging just so we can dump
>                system core.
  A contiguous file or block table gets you both.



--

  :!mcr!:
  Michael Richardson                     Amiga
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