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

William Lee Irwin III
2004-11-20T02:03:06Z

On Fri, Nov 19, 2004 at 11:59:03AM -0800, Linus Torvalds wrote:
> 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.

Unprivileged triggers for full-tasklist scans are NMI oops material.

-- wli