Re: dentry bloat.

From: Dipankar Sarma
Date: Sat May 08 2004 - 16:23:22 EST

On Sat, May 08, 2004 at 01:55:12PM -0700, Andrew Morton wrote:
> Dipankar Sarma <dipankar@xxxxxxxxxx> wrote:
> > There are couple of issues that need to be checked -
> >
> > 1. Re-doing the parent comparison and full name under ->d_lock
> > need to be benchmarked using dcachebench. That part of code
> > is extrememly performance sensitive and I remember that the
> > current d_movecount based solution was done after a lot of
> > benchmarking of various alternatives.
> There's a speed-space tradeoff here as well. Making the dentry smaller
> means that more can be cached, which reduces disk seeks. On all
> machines...

Another thing that would help is the singly linked rcu patch.
It shaves off 8-bytes per-rcu_head on x86. Should I revive
that ?

> But yes, when I've finished mucking with this I'll be asking you to put it
> all through your performance/correctness/stress tests please.

Yes, sure.

> One thing which needs to be reviewed is the layout of the dentry, too.

IIRC, Maneesh did some experiments with this and found that any
changes in the layout he did only degraded performance :)

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