linux-kernel - Re: [PATCH 1/4] stringbuf: A string buffer implementation

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Message-ID: <20071026205714.GQ17536@waste.org>
Date:	Fri, 26 Oct 2007 15:57:14 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH 1/4] stringbuf: A string buffer implementation

On Fri, Oct 26, 2007 at 05:57:27AM -0600, Matthew Wilcox wrote:
> On Fri, Oct 26, 2007 at 12:11:01PM +1000, Rusty Russell wrote:
> > 	This just seems like more optimization and complexity that we need.  Interfaces
> > using vsnprintf don't seem like good candidates for optimization.
> 
> That's a fair point, but I'm optimising for fewer trips into the
> slab(/slub/slob) allocator, and thus having less of an impact on the
> rest of the system.  Given that 'an alloc on every call' was one of the
> complaints Matt had about my v1 stringbuf patch, I can't imagine he'll
> be happy about this one either.

Well I expect once you start letting people easily build strings by
concatenation, you'll very shortly afterwards have people using them
in loops. And having hidden O(n^2) behavior in there is a little sad,
even though n will tend to be small and well-bounded. If we can do
something simple to avoid it, we should.

-- 
Mathematics is the supreme nostalgia of our time.
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