Re: [rfc][patch] dynamic resizing dentry hash using RCU

From: William Lee Irwin III
Date: Fri Feb 23 2007 - 23:25:15 EST

On Fri, Feb 23, 2007 at 04:37:43PM +0100, Nick Piggin wrote:
> The dentry hash uses up 8MB for 1 million entries on my 4GB system is
> one of the biggest wasters of memory for me. Because I rarely have
> more than one or two hundred thousand dentries. And that's with
> several kernel trees worth of entries. Most desktop and probably even
> many types of servers will only use a fraction of that.
> So I introduce a new method for resizing hash tables with RCU, and apply
> that to the dentry hash.
> The primitive heuristic is that the hash size is doubled when the number of
> entries reaches 150% the hash size, and halved when the number is 50%.
> It should also be able to shrink under memory pressure, and scale up as
> large as we go.

You would be better served by a data structure different from a hashtable.

-- wli
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