From: Arnd Bergmann <arnd@arndb.de>
To: =?iso-8859-1?q?J=F6rn_Engel?= <joern@wohnheim.fh-wedel.de>
Subject: Re: [RFC] Alignment of fields in struct dentry
Date: Fri, 15 Sep 2006 22:44:07 +0200
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Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20060914093123.GA10431@wohnheim.fh-wedel.de> <20060914215545.GC6441@schatzie.adilger.int> <20060915102736.GA767@wohnheim.fh-wedel.de>
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Am Friday 15 September 2006 12:27 schrieb J?rn Engel:
> -};
> +}__attribute__((aligned(64)));?/* make sure the dentry is 128/192 bytes
> +??????????????????????????????? ? on 32/64 bit independently of config
> +??????????????????????????????? ? options. ?d_iname will vary in length
> +??????????????????????????????? ? a bit. */

I'd guess that a 32 byte alignment is much better here, 64 byte sounds
excessive. It should have the same effect with the current dentry layout
and default config options, but would keep the d_iname length in the
16-44 byte range instead of 16-76 byte as your patch does.

Since all important fields are supposed to be kept in 32 bytes anyway,
they are still either at the start or the end of a given cache line,
but never cross two.

	Arnd <><
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