From: Rich Felker <dalias@aerifal.cx>
To: musl@lists.openwall.com
Subject: Re: unneeded mremap calls in realloc
Date: Wed, 16 Nov 2011 21:50:31 -0500 [thread overview]
Message-ID: <20111117025031.GR132@brightrain.aerifal.cx> (raw)
In-Reply-To: <20111116004536.GV24939@port70.net>
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...
Rich
next prev parent reply other threads:[~2011-11-17 2:50 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-16 0:45 Szabolcs Nagy
2011-11-17 2:50 ` Rich Felker [this message]
2011-11-17 5:02 ` Rich Felker
2011-11-17 12:31 ` Szabolcs Nagy
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