Re: [reiserfs-dev] Re: Note describing poor dcache utilization under high memory pressure

From: Josh MacDonald (jmacd@CS.Berkeley.EDU)
Date: Tue Jan 29 2002 - 12:28:58 EST


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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