Re: page fault scalability patch V11 [0/7]: overview

[Linus Torvalds]

On Fri, 19 Nov 2004, Christoph Lameter wrote:
> 
> Note that I have posted two other approaches of dealing with the rss problem:

You could also make "rss" be a _signed_ integer per-thread.

When unmapping a page, you decrement one of the threads that shares the mm 
(doesn't matter which - which is why the per-thread rss may go negative), 
and when mapping a page you increment it.

Then, anybody who actually wants a global rss can just iterate over
threads and add it all up. If you do it under the mmap_sem, it's stable,
and if you do it outside the mmap_sem it's imprecise but stable in the
long term (ie errors never _accumulate_, like the non-atomic case will 
do).

Does anybody care enough? Maybe, maybe not. It certainly sounds a hell of 
a lot better than the periodic scan.

		Linus
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