Re: 128MB Swap-Space Limit

Marnix Coppens (maco@telindus.be)
Tue, 11 Aug 1998 17:24:48 +0200


At 15:37 11/08/98 +0200, Thomas Scheunemann wrote:
>
>Is there any deeper reason, why a single swap-space is limited to 128MB (on
>i386)?
>

Note: this is from memory (and swapped back in, now).
Swapping is done by pages, 4KB at a time. A separate page of 4KB is used
by the kernel as a bitmap to describe the state of the various pages
inside the swap file. Such a bitmap contains 32K bits, each bit describing
the validity of a 4KB piece of the swapfile. Therefore, swapfiles are
limited to 32K*4KB = 128MB.

And yes, it's easy to enhance this. Either you keep more pages for your
swap bitmap or you activate more than one swapfile.
Not much difference, really.

HTH,

Marnix Coppens

---
Reality is that which                   | Artificial Intelligence
when you stop believing                 | stands no chance against
in it doesn't go away. (Philip K. Dick) | Natural Stupidity.

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