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From: Daniel Phillips <phillips@arcor.de>
To: Andrew Morton <akpm@zip.com.au>
Subject: Re: [RFC] [PATCH] Include LRU in page count
Date: Mon, 2 Sep 2002 00:20:49 +0200
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Cc: Christian Ehrhardt <ehrhardt@mathematik.uni-ulm.de>,
       Linus Torvalds <torvalds@transmeta.com>,
       Marcelo Tosatti <marcelo@conectiva.com.br>,
       linux-kernel@vger.kernel.org
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On Monday 02 September 2002 00:09, Andrew Morton wrote:
> Daniel Phillips wrote:
> > 
> > ...
> > I'm looking at your spinlock_irq now and thinking the _irq part could
> > possibly be avoided.  Can you please remind me of the motivation for this -
> > was it originally intended to address the same race we've been working on
> > here?
> 
> scalability, mainly.  If the CPU holding the lock takes an interrupt,
> all the other CPUs get to spin until the handler completes.  I measured
> a 30% reducton in contention from this.
> 
> Not a generally justifiable trick, but this is a heavily-used lock.
> All the new games in refill_inactive() are there to minimise the
> interrupt-off time.

Ick.  I hope you really chopped the lock hold time into itty-bitty pieces.

Note that I changed the spin_lock in page_cache_release to a trylock, maybe
it's worth checking out the effect on contention.  With a little head 
scratching we might be able to get rid of the spin_lock in lru_cache_add as
well.  That leaves (I think) just the two big scan loops.  I've always felt
it's silly to run more than one of either at the same time anyway.

-- 
Daniel
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