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Postings from July 2010
On Fri, Jul 30, 2010 at 9:37 AM, Wolfram Humann <w.c.humann@arcor.de> wrote:
> I would like to propose that perl requests an additional amount of memory
> from realloc when strings grow by a small amount.
+1 -- though I'm not clear whether this win32 specific or whether all
operating systems should work this way.
> if (newlen > SvLEN(sv)) { /* need more room? */
> size_t minlen = SvCUR(sv);
> minlen += (minlen >> PERL_STRLEN_EXPAND_SHIFT) + 10;
> if (newlen < minlen) newlen = minlen;
[snip]
I have a few questions about the specific implementation. Please
don't take them as suggestions that your approach is necessarily wrong
-- but I'd like to understand the logic behind certain choices.
* Why are you suggesting making the extra allocation proportional to
the length of the string? Why not a multiple of the length of the
increment? Why not a fixed amount?
* Why the "+10"? Why have a extra minimum at all? Why "10" instead
of another number? Given your examples, for a large string the 10 is
a trivial fraction of the total and for a small string, the efficiency
either doesn't matter or the string quickly grows into a large string
anyway.
* Why do you think PERL_STRLEN_EXPAND_SHIFT should be 2? That's a 25%
increase in the length of the string. (In many programs, I suspect
many strings are appended to only a few times and that seems like
large memory price to pay.)
> On current Strawberry Perl (5.10 or 5.12):
> a) 2.6 seconds
> b) 18 seconds
>
> Perl 5.12 compiled on win32 with modifications as above:
> a) 0.014 seconds
> b) 0.2 seconds
Awesome! What does it look like with a shift of 3 or 4?
-- David
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