Thanks to all who responded with useful comments.

It isn't entirely clear from the comments when gimp starts up, but the tiling cache should indeed be almost as large as physical memory, allowing some for other uses (such as the OS).

Increasing to 1500Mb on a 2G system was a huge improvement. I have not sought to tune that number, not doing enough of these to make that worthwhile. The undo suggestion of Alastair Robinson is also probably very good for continued manipulation.

As I think the original posting indicated, allowing virtual memory to do the work, is for whatever reason not the answer.

I suggest modifying the documentation to read something like:

Increasing tile memory cache will continue to yield benefits until you totally saturate physical memory. If you can afford to give nearly all your physical memory to gimp while you are running it, and you need to process large images, then do so.

thanks, Dov

If the OS has better virtual memory than what available to gimp, >then

you would want to use that one. In Linux, I think in most >cases, you would want to use the (often in multiple disks) swap >partitions/files available to the OS.

Evidently not, as in my first post.