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SubjectRe: [PATCH 0/2] pdflush fix and enhancement
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On Wed, 2008-12-31 at 14:27 +0100, Andi Kleen wrote:
> > I say most because the assumption would be that we will be successful in
> > creating the new thread. Not that bad an assumption I think. Besides,
>
> And that the memory read is not reordered (rmb()).
>

At the risk of showing my b*tt here... I'm not very clear on memory
barriers, is this necessary even inside a critical region? (recall
we're protected by the spin lock). If so, does the barrier go after the
read, or before? (Thanks for not laughing, however grins are allowed)


>
> Ok it probably needs some kind of feedback mechanism.
>

Actually, I tend to think we need an entirely different approach to
flushing, please see my post to David Chinner which outlines some
thoughts. Basically a flushing heuristic that takes into account the
characteristics of the various block devices.


> >
> > I was thinking about a patch that would go both directions - forward and
> > reverse depending upon, say, a bit in jiffies... Certainly not perfect,
> > but a bit more fair.
>
> Better a real RNG. But such probalistic schemes unfortunately tend to drive
> benchmarkers crazy, that is why it is better to avoid them.
>

Nod, but that's ok. Having been one for several years I can truthfully
say that benchmarkers are a little crazy anyways... :-)


> I suppose you could just keep some state per fs to ensure fairness.
>

Nod, this would be ideal.

-PWM

> -Andi



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