linux-kernel - Re: [PATCH] fs: Add romfs version 2

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Date:	Mon, 6 Aug 2007 12:20:03 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Lindsay Roberts <lindsay.roberts.os@...il.com>
Cc:	Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	celinux-dev@...e.celinuxforum.org
Subject: Re: [PATCH] fs: Add romfs version 2

On Mon, Aug 06, 2007 at 05:43:54PM +1000, Lindsay Roberts wrote:
> On 7/26/07, Pavel Machek <pavel@....cz> wrote:
> > If the fs is read-only.. can we do some tail packing and get _both_
> > speed and space efficiency?
> 
> You mean don't block align files of size less than 1k, and
> intelligently pack them into the gaps left by files that are aligned?
> Does seem that most noticeable performance issues occur on sequential
> reads of large files, this sounds like a good idea, but I would
> welcome comments on this.
> 
> Also I assume romfs currently has a small hidden benefit as a result
> of it storing its file data serially after the inode: the initial read
> of the inode reads and therefore caches the block containing the
> (initial) file data. Obviously with block aligned file data this only
> applies if sequential prefetching is performed. I'd be interested to
> know if this is an issue worth regarding.

It seems to me that the initial design goals of romfs were:

a) space efficiency
b) simplicity

..with performance basically ignored. On an actual ROM-backed
filesystem, alignment doesn't help you until it becomes large enough
that you can execute pages in place.

And I don't think your reproduceability concern was even on the radar.
So naming a new filesystem romfs which has the priorities:

a) performance
b) reproduceability

seems like it's going to disappoint and confuse people who were
aligned with the original goals.

-- 
Mathematics is the supreme nostalgia of our time.
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