linux-kernel - Re: [PATCH] fs : reorder some 'struct inode' fields to speedup i

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Message-Id: <20061127140131.0353bbca.akpm@osdl.org>
Date:	Mon, 27 Nov 2006 14:01:31 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs : reorder some 'struct inode' fields to speedup
 i_size manipulations

On Mon, 27 Nov 2006 22:52:04 +0100
Eric Dumazet <dada1@...mosbay.com> wrote:

> > I didn't understand that paragraph at all, really, so I took it out.
> > 
> > At present an i_size change will dirty one, two or three cachelines, most
> > likely one or two.
> > 
> > After your patch an i_size change will dirty one or two cachelines, most
> > likely one.
> > 
> > yes?
> 
> nope
> 
> Before :
> ---------
>   offsetof(i_size) = 0x3C
> 
> i_size is 8 bytes, so i_size spans 2 cache lines (if 64 or 32 bytes cache lines)

This all depends on the offset of the inode, and you don't know what that is.

offsetof(ext3_inode_info, vfs_inode) != offsetof(nfs_inode, vfs_inode), etc.
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