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| From | "BartC" <bc@freeuk.com> |
|---|---|
| Newsgroups | comp.lang.c |
| References | <911c685c-3bf9-4079-bf61-66342d8a8c2c@u6g2000vbc.googlegroups.com> <20111231091520.131@kylheku.com> <67cb95d9-a8ef-4e34-9def-a5163e008862@n6g2000vbg.googlegroups.com> <f7s5t8-jo5.ln1@voyager.wichi.de.vu> |
| Subject | Re: Memory management and custom allocator |
| Message-ID | <LPYLq.355$EO5.173@newsfe26.ams2> (permalink) |
| Organization | virginmedia.com |
| Date | 2012-01-01 12:54 +0000 |
"Markus Wichmann" <nullplan@gmx.net> wrote in message
news:f7s5t8-jo5.ln1@voyager.wichi.de.vu...
> On 31.12.2011 18:52, FtM wrote:
>> Simply because it can't know if I'm going to do 200 little allocations
>> or 1 big one.
> For one, it _never_ uses brk(). That syscall is just plain old and does
> nothing mmap() couldn't do better. Then it has linked lists prepared for
> objects of sizes of powers of two, starting at 16 and stopping at 2048.
That exactly what I do in my own allocator! Except I stop at 1024. Although
I probably manage them very differently, for example once a small block size
is allocated, say 64 bytes, it always stays that size.
And one thing about malloc() I don't like, are the overheads in having to
remember the block sizes; if I allocate 16 bytes, malloc() seems to reserve
either 20 or, more often, 24 bytes on the few compilers I've tried. That's a
50% overhead!
Also if you're being sensible and trying to keep to power-of-two
allocations, this 4- or 8-byte overhead is going to screw that up.
My allocators have never stored a block size, and it has never really been a
problem. Either you will know the size (a struct for example), or you need
to keep track of it yourself, in which case it is very handy when you have
an allocation that can grow in never having to keep running back to
realloc().
As an illustration, take this simple example of a string growing from one to
ten million characters:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
char *p;
int i,len;
p=malloc(1);
*p=0;
len=0;
for (i=1; i<=10000000; ++i) {
++len;
p=realloc(p,len+1);
p[len-1]='*';
p[len]=0;
// puts(p);
}
printf("Length= %d\n",strlen(p));
}
On three C compilers, this took about 12 seconds (on DMC, any length of
string resulted in a runtime of 0.4 seconds; a bit odd).
Using my strategy, of avoiding any calls to malloc or realloc unless
absolutely necessary, and using that inside an interpreter, this bit of
script took about 0.1 seconds:
string a
a:=""
to 10 million do
a+:="*"
od
println "Length=",a.len
Of course, real C code wouldn't use such a naive strategy; it would also
seek to minimise malloc()/realloc() calls, but that's also an admission that
these calls have some overheads which it would be desirable to avoid. Hence
I can understand the OP's attempt to experiment with his own versions.
--
Bartc
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[Slightly OT] Memory management and custom allocator FtM <fmassei@gmail.com> - 2011-12-31 06:56 -0800
Re: [Slightly OT] Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-12-31 11:08 -0500
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2011-12-31 08:28 -0800
Re: [Slightly OT] Memory management and custom allocator Johann Klammer <klammerr@NOSPAM.aon.at> - 2011-12-31 17:39 +0100
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2011-12-31 08:55 -0800
Re: Memory management and custom allocator Johann Klammer <klammerr@NOSPAM.aon.at> - 2011-12-31 19:01 +0100
Re: Memory management and custom allocator Kaz Kylheku <kaz@kylheku.com> - 2011-12-31 18:31 +0000
Re: [Slightly OT] Memory management and custom allocator Kaz Kylheku <kaz@kylheku.com> - 2011-12-31 17:24 +0000
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2011-12-31 09:52 -0800
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-12-31 14:30 -0500
Re: Memory management and custom allocator Markus Wichmann <nullplan@gmx.net> - 2012-01-01 12:21 +0100
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-01 12:54 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-01 09:03 -0500
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-01 16:23 +0000
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-01 21:41 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-02 08:10 -0500
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 14:07 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-02 09:47 -0500
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 08:36 -0800
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-02 13:43 -0500
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 11:38 -0800
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-03 13:14 +0000
Re: Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-03 06:07 -0800
Re: Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-05 17:06 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 21:36 +0000
Re: Memory management and custom allocator Kaz Kylheku <kaz@kylheku.com> - 2012-01-02 21:44 +0000
Re: Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-02 23:10 -0800
Re: Memory management and custom allocator Keith Thompson <kst-u@mib.org> - 2012-01-02 13:42 -0800
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-02 17:38 -0500
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-02 21:45 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-02 18:19 -0500
Re: Memory management and custom allocator Keith Thompson <kst-u@mib.org> - 2012-01-02 15:42 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 23:59 +0000
Re: Memory management and custom allocator Kleuske <kleuske@nowhere.net> - 2012-01-03 11:38 +0000
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-03 12:49 +0000
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-04 23:42 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-04 20:23 -0500
Re: Memory management and custom allocator Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-01-05 23:31 +0200
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-04 21:52 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-04 20:31 -0500
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-05 01:45 +0000
Re: Memory management and custom allocator Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-01-07 05:55 +0200
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-07 12:02 +0000
Re: Memory management and custom allocator Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-01 09:08 -0500
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-01 10:08 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-01 23:34 +0000
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 02:18 -0800
Re: Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-02 02:34 -0800
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 02:43 -0800
Re: Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-02 03:11 -0800
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 08:17 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 11:40 +0000
Re: Memory management and custom allocator FtM <fmassei@gmail.com> - 2012-01-02 08:27 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-01 23:26 +0000
Re: Memory management and custom allocator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-01 23:54 +0000
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 00:32 +0000
Re: Memory management and custom allocator Kaz Kylheku <kaz@kylheku.com> - 2012-01-02 02:46 +0000
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-02 11:53 +0000
Re: Memory management and custom allocator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-01-02 15:18 +0000
Re: Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-03 12:21 +0000
Re: Memory management and custom allocator Karl Malbrain <malbrain@yahoo.com> - 2012-01-04 16:48 -0800
Re: Memory management and custom allocator "BartC" <bc@freeuk.com> - 2012-01-05 01:36 +0000
Re: [Slightly OT] Memory management and custom allocator "io_x" <a@b.c.invalid> - 2012-01-01 17:02 +0100
Re: [Slightly OT] Memory management and custom allocator jgk@panix.com (Joe keane) - 2012-01-01 21:21 +0000
Re: [Slightly OT] Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-01 21:01 -0800
Re: [Slightly OT] Memory management and custom allocator 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-07 05:20 -0800
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