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Date: Wed, 16 Nov 2011 21:50:31 -0500
From: Rich Felker <>
Subject: Re: unneeded mremap calls in realloc

On Wed, Nov 16, 2011 at 01:45:37AM +0100, Szabolcs Nagy wrote:
> as discussed on irc, in realloc there is a mremap
> where newlen is pagesize adjusted but oldlen is not
> so oldlen==newlen almost always fails
> run this simple test case with strace to see the issue:
> #include <stdlib.h>
> int main(){
> 	char *p = 0;
> 	int n;
> 	for (n = 0; n < 500000; n++)
> 		p = realloc(p, n);
> 	free(p);
> 	return 0;
> }
> the fix that significantly speeds up the above code:
> (there might be better fix, eg why oldlen is not a
> multiple of pagesize in the first place?)

oldlen should always be a multiple of page size.. Need to check out
why it's not...


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