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

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Message-ID: <20070224042444.GU21484@holomorphy.com>
Date:	Fri, 23 Feb 2007 20:24:44 -0800
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [rfc][patch] dynamic resizing dentry hash using RCU

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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