linux-kernel - Re: [PATCH 15/18] fs: introduce a per-cpu last

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Message-ID: <20101008191047.GA29976@infradead.org>
Date:	Fri, 8 Oct 2010 15:10:47 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	Dave Chinner <david@...morbit.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/18] fs: introduce a per-cpu last_ino allocator

On Fri, Oct 08, 2010 at 04:06:12PM +0200, Eric Dumazet wrote:
> On 32bit arches, inum for sockets/pipes could be pretty fast
> 
> unsigned u32 rnd_val __read_mostly; /* seeded at boot time */
> 
> unsigned u32 get_inum(struct inode *ino, size_t size)
> {
> 	return rnd_val ^ ((long)ino + random32() % size);
> }
> 
> (Ie , use fact that an inode is a kernel object, with a given address
> and a given size, two inodes cannot overlap)

Yeah, we could probably do this.  From looking at the remaining users
of the last_ino replacement this could probably work for them.

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