linux-kernel - Re: swap-prefetch: 2.6.22 -mm merge plans

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Date:	Thu, 10 May 2007 17:04:54 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Ray Lee <ray-lk@...rabbit.org>
CC:	Con Kolivas <kernel@...ivas.org>, Ingo Molnar <mingo@...e.hu>,
	ck list <ck@....kolivas.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: swap-prefetch: 2.6.22 -mm merge plans

Ray Lee wrote:
> On 5/9/07, Nick Piggin <nickpiggin@...oo.com.au> wrote:
> 
>> Ray Lee wrote:
>> > On 5/9/07, Nick Piggin <nickpiggin@...oo.com.au> wrote:
>> >
>> >> You said it helped with the updatedb problem. That says we should 
>> look at
>> >> why it is going bad first, and for example improve use-once 
>> algorithms.
>> >> After we do that, then swap prefetching might still help, which is 
>> fine.
>> >
>> > Nick, if you're volunteering to do that analysis, then great. If not,
>> > then you're just providing a airy hope with nothing to back up when or
>> > if that work would ever occur.
>>
>> I'd like to try helping. Tell me your problem.
> 
> 
> Huh? You already stated one version of it above, namely updatedb. But

So a swapping problem with updatedb should be unusual and we'd like to see
if we can fix it without resorting to prefetching.

I know the theory behind swap prefetching, and I'm not saying it doesn't
work, so I'll snip the rest of that.


>> What's wrong with the use-once we have? What improvements are you talking
>> about?
> 
> 
> You said, effectively: "Use-once could be improved to deal with
> updatedb". I said I've been reading emails from Rik and others talking
> about that for four years now, and we're still talking about it. Were
> it merely updatedb, I'd say us userspace folk should step up and
> rewrite the damn thing to amortize its work. However, I and others
> feel it's only an example -- glaring, obviously -- of a more pervasive
> issue. A small issue, to be sure!, but an issue nevertheless.

It isn't going to get fixed unless people complain about it. If you
cover the use-once problem with swap prefetching, then it will never
get fixed.


>> I don't think it is about energy or being mean, I'm just stating the
>> issues I have with it.
> 
> 
> Nick, I in no way think you're being mean, and I'm sorry if I've given
> you that impression. However, if you're just stating the issues you
> have with it, then can I assume that you won't lobby against having
> this experiment merged?

Anybody is free to merge anything into their kernel. And if somebody
asks for my issues with the swap prefetching patch, then I'll give
them :)

-- 
SUSE Labs, Novell Inc.
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