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

[Nick Piggin]

William Lee Irwin III wrote:
> 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.

Hang on, let's come back to this...

We already have unprivileged do-for-each-thread triggers in the proc
code. It's in do_task_stat, even. Rss reporting would basically just
involve one extra addition within that loop.

So... hmm, I can't see a problem with it.
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