Re: [PATCH] Decrease hash table memory overhead

From: Oliver Xymoron (oxymoron@waste.org)
Date: Mon Jul 31 2000 - 15:39:51 EST


On Mon, 31 Jul 2000, Andi Kleen wrote:

> On Mon, Jul 31, 2000 at 08:00:28PM +0200, Linus Torvalds wrote:
> >
> > "Doing it from user space might show that it's not a performance
> > optimization that cna be noticed".
>
> Or it might. It is just too much work for me, because it is takes too long
> to do right.
>
> I believe when you manage to save 200K of active L2 cache lines from kernel
> use, then a user with a 512K L2 cache will notice it. The hlists are
> hopefully good for 20-40K. It would be a beginning at least.

You have to be hitting the inode cache pretty hard for this to be a big
deal, right? And that cache is already hidden behind the dcache, right?
I think the saving memory side of your argument is better than the cache
footprint one..

Perhaps there's another clever way to do this - is there a way to make the
list heads partially overlap? That is &hash[i-1].next == &hash[i].prev?
Sick, I know, but it might not mean a separate list implementation, just
special initialization - HASHLISTHEAD().

--
 "Love the dolphins," she advised him. "Write by W.A.S.T.E.." 

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