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From: torvalds@transmeta.com (Linus Torvalds)
To: linux-kernel@vger.kernel.org
Subject: Re: dentry cache order 7 is broken
Date: 8 Feb 2001 17:21:20 -0800	[thread overview]
Message-ID: <95vgmg$i9u$1@penguin.transmeta.com> (raw)
In-Reply-To: <Pine.LNX.4.33.0102072302030.5947-100000@twinlark.arctic.org>

In article <Pine.LNX.4.33.0102072302030.5947-100000@twinlark.arctic.org>,
dean gaudet  <dean-list-linux-kernel@arctic.org> wrote:
>
>if you've got 512Mb of RAM you end up with a dentry cache of order 7 --
>65536 entries.
>
>this results in a D_HASHBITS of 16.  if you look at d_hash it contains
>this code:
>
>	hash = hash ^ (hash >> D_HASHBITS) ^ (hash >> D_HASHBITS*2);

Cool.

Just remove the third part altogether.  The "hash" is only 32 bits
anyway (even on 64-bit platforms, as we don't want to blow up the dentry
size unnecessarily).  And with most machines with reasonable memory, you
already get fine distribution with just two terms (ie you don't lose any
bits), and it speeds it up and avoids the problem you see.

Thanks..

		Linus
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      parent reply	other threads:[~2001-02-09  1:21 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2001-02-08  7:15 dentry cache order 7 is broken dean gaudet
2001-02-08  8:10 ` David S. Miller
2001-02-08  8:22   ` Mitchell Blank Jr
2001-02-08  9:22     ` David S. Miller
2001-02-09  0:36   ` dean gaudet
2001-02-09  1:21 ` Linus Torvalds [this message]

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