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

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Message-ID: <20071024152036.GX19691@waste.org>
Date:	Wed, 24 Oct 2007 10:20:36 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH 1/4] stringbuf: A string buffer implementation

On Tue, Oct 23, 2007 at 07:49:20PM -0600, Matthew Wilcox wrote:
> On Tue, Oct 23, 2007 at 05:11:16PM -0500, Matt Mackall wrote:
> > You might want to consider growing the buffer by no less than a small
> > constant factor like 1.3x. This will keep things that do short concats
> > in a loop from degrading to O(n^2) performance due to realloc and
> > memcpy.
> 
> I looked at slab and slub, and would grow the buffer by no less than
> 1.5x each time, thanks to the buckets.  I'd initially implemented 2x,
> but switched to allocating size+1 and calling ksize() as being a more
> efficient implementation.

Fair enough.
 
> I presume slob is different?  Actually, slob doesn't seem to
> provide krealloc, so I think stringbuf won't work on slob.  Will you
> have time to fix this?

http://lxr.linux.no/source/mm/slob.c#L207

Yep, slob is different, it has no kmalloc buckets.

> > Should probably just bite the bullet and pass a flag.
> 
> Hrm.
> 
> extern void sb_printf(struct stringbuf *sb, gfp_t gfp, const char *fmt, ...)
>         __attribute__((format(printf, 3, 4)));
> 
> ?  Any objections?

Fine by me.
 
> > > +#define INITIAL_SIZE 32
> > 
> > Too small. That will guarantee that most users end up doing a realloc.
> > Can we have 128 instead?
> 
> I don't care.  Sure!

Most of these objects will have very short lifetimes, so there's very
little downside.

-- 
Mathematics is the supreme nostalgia of our time.
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