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Date: Fri, 19 Nov 2004 18:41:04 -0800
From: William Lee Irwin III <wli@holomorphy.com>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Linus Torvalds <torvalds@osdl.org>, Christoph Lameter <clameter@sgi.com>,
       akpm@osdl.org, Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Hugh Dickins <hugh@veritas.com>, linux-mm@kvack.org,
       linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: page fault scalability patch V11 [0/7]: overview
Message-ID: <20041120024104.GE2714@holomorphy.com>
References: <Pine.LNX.4.58.0411181715280.834@schroedinger.engr.sgi.com> <419D581F.2080302@yahoo.com.au> <Pine.LNX.4.58.0411181835540.1421@schroedinger.engr.sgi.com> <419D5E09.20805@yahoo.com.au> <Pine.LNX.4.58.0411181921001.1674@schroedinger.engr.sgi.com> <1100848068.25520.49.camel@gaston> <Pine.LNX.4.58.0411190704330.5145@schroedinger.engr.sgi.com> <Pine.LNX.4.58.0411191155180.2222@ppc970.osdl.org> <20041120020306.GA2714@holomorphy.com> <419EAB21.8020207@yahoo.com.au>
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William Lee Irwin III wrote:
>> Unprivileged triggers for full-tasklist scans are NMI oops material.

On Sat, Nov 20, 2004 at 01:25:37PM +1100, Nick Piggin wrote:
> What about pushing the per-thread rss delta back into the global atomic
> rss counter in each schedule()?
> Pros:
> This would take the task exiting problem into its stride as a matter of
> course.
> Single atomic read to get rss.
> Cons:
> would just be moving the atomic op somewhere else if we don't get
> many page faults per schedule.
> Not really nice dependancies.
> Assumes schedule (not context switch) must occur somewhat regularly.
> At present this is not true for SCHED_FIFO tasks.
> Too nasty?

This doesn't sound too hot. There's enough accounting that can't be
done anywhere but schedule(), and this can be done elsewhere. Plus,
you're moving an already too-frequent operation to a more frequent
callsite.


-- wli