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

Matt Mackall
2007-10-24T15:21:11Z

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.