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Date: Wed, 06 Jun 2001 14:57:29 -0700
From: LA Walsh <law@sgi.com>
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To: "Eric W. Biederman" <ebiederm@xmission.com>
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Subject: Re: Break 2.4 VM in five easy steps
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"Eric W. Biederman" wrote:

> The hard rule will always be that to cover all pathological cases swap
> must be greater than RAM.  Because in the worse case all RAM will be
> in thes swap cache.  That this is more than just the worse case in 2.4
> is problematic.  I.e. In the worst case:
> Virtual Memory = RAM + (swap - RAM).

Hmmm....so my 512M laptop only really has 256M?  Um...I regularlly run
more than 256M of programs.  I don't want it to swap -- its a special, weird
condition if I do start swapping.  I don't want to waste 1G of HD (5%) for
something I never want to use.  IRIX runs just fine with swap<RAM.  In
Irix, your Virtual Memory = RAM + swap.  Seems like the Linux kernel requires
more swap than other old OS's (SunOS3 (virtual mem = min(mem,swap)).
I *thought* I remember that restriction being lifted in SunOS4 when they
upgraded the VM.  Even though I worked there for 6 years, that was
6 years ago...

> You can't improve the worst case.  We can improve the worst case that
> many people are facing.

---
    Other OS's don't have this pathological 'worst case' scenario.  Even
my Windows [vm]box seems to operate fine with swap<MEM.  On IRIX,
virtual space closely approximates physical + disk memory.

> It's worth complaining about.  It is also worth digging into and find
> out what the real problem is.  I have a hunch that this hole
> conversation on swap sizes being irritating is hiding the real
> problem.

---
    Okay, admission of ignorance.  When we speak of "swap space",
is this term inclusive of both demand paging space and
swap-out-entire-programs space or one or another?
-linda

--
The above thoughts and           | They may have nothing to do with
writings are my own.             | the opinions of my employer. :-)
L A Walsh                        | Trust Technology, Core Linux, SGI
law@sgi.com                      | Voice: (650) 933-5338