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Date: Tue, 29 Jan 2002 09:28:58 -0800
From: Josh MacDonald <jmacd@CS.Berkeley.EDU>
To: Alexander Viro <viro@math.psu.edu>
Cc: Hans Reiser <reiser@namesys.com>,
        Daniel Phillips <phillips@bonn-fries.net>,
        Linus Torvalds <torvalds@transmeta.com>,
        Josh MacDonald <jmacd@CS.Berkeley.EDU>, linux-kernel@vger.kernel.org,
        reiserfs-list@namesys.com, reiserfs-dev@namesys.com
Subject: Re: [reiserfs-dev] Re: Note describing poor dcache utilization under high memory pressure
Message-ID: <20020129092858.D8740@helen.CS.Berkeley.EDU>
In-Reply-To: <3C55E9E3.50207@namesys.com> <Pine.GSO.4.21.0201281927320.6592-100000@weyl.math.psu.edu>
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In-Reply-To: <Pine.GSO.4.21.0201281927320.6592-100000@weyl.math.psu.edu>; from viro@math.psu.edu on Mon, Jan 28, 2002 at 07:30:37PM -0500
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Quoting Alexander Viro (viro@math.psu.edu):
> 
> 
> On Tue, 29 Jan 2002, Hans Reiser wrote:
> 
> > This fails to recover an object (e.g. dcache entry) which is used once, 
> > and then spends a year in cache on the same page as an object which is 
> > hot all the time.  This means that the hot set of objects becomes 
> > diffused over an order of magnitude more pages than if garbage 
> > collection squeezes them all together.  That makes for very poor caching.
> 
> Any GC that is going to move active dentries around is out of question.
> It would need a locking of such strength that you would be the first
> to cry bloody murder - about 5 seconds after you look at the scalability
> benchmarks.

We're not talking about actively referenced entries, we're talking about
entries on the d_lru list with zero references.  Relocating those objects
should not require any more locking than currently required to remove and
re-insert the dcache entry.  Right?

-josh

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