RFC: How to write a page to swap with [near] zero impact on memory?

[Nigel Cunningham <ncunningham@clear.net.nz>]

Hi all.

I'm beginning to port the 2.4 beta 18 version, which allows the user to
suspend to disk what is pretty close to a complete image of RAM at the
time the suspend is initiated. Since this implies working in conditions
where there might be only a few hundred pages available, I carefully
accounted for pages in use and worked to free buffers and swapcache
pages that were added during the image-saving process. I'm wanting to
implement the same thing under 2.5, and would like advice on the best
way to do it. (Ideally, I'd like to write a page and have everything at
the end exactly as it was at the start, except that a copy of the page
is on disk as well as in memory).

I've spent some time looking at mm/*.c, but I won't pretend for a moment
to have a fraction of the knowledge that you guys have. I thus thought
I'd be wise to talk with you all before I submit any patches for
comments. What suggestions would you provide about minimising the impact
of writing a page to swap? 

Thanks in advance for any help and regards,

Nigel

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