Ram & swap, Was: [H-GEN] Linux & NTFS

[Paul Gearon]

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On Tue, 17 Dec 2002 ben.carlyle at invensys.com wrote:

> Personally I've usually gone for something like ram=swap on systems
> I've had opportunity to make such decisions about.

I'll confess that I haven't paid attention to the VMM for the last 3
months, but I'm pretty sure it hasn't changed yet.

The current memory algorithm in the VMM reserves swap space whenever
memory is allocated.  That way, any part of a processes memory has a
section of swap space set aside for it, needed or not.

The result is actually quite fast, but it means that if you only have a
swap space that it equal to or less than the size of your RAM then there
is no space left over for swapping memory in and out.  ie. If your swap is
<= size of RAM then don't bother with swap at all (you DON'T get any extra
available memory from it, and it will actually slow you down).  Anything
larger than the size of your RAM provides some benifit.

Linus's suggestion is for swap to be twice the size of RAM, but that's
just him.  :-)

Linus *did* go on to say that they're looking at a different swap
algorithm (one that benifits from small swap files), but it's definately
not in the 2.4.x series.

Regards,
Paul Gearon

Software Engineer                Telephone:   +61 7 3876 2188
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