sbrk(2) broken

Poul-Henning Kamp phk at
Fri Jan 4 04:57:13 PST 2008

In message <20080104122149.GA17103 at>, Andrey Chernov writes:
>On Wed, Jan 02, 2008 at 10:38:40PM -0800, Jason Evans wrote:
>> Poul-Henning noticed today that xchat fails to start if malloc uses sbrk 
>> internally.  
>Malloc() itself knows about memory amount _really_ in use by a program [...]

No, the VM system has a much better idea about this.

You need to think about this the right way:

There is address space allocated to the process (via sbrk/mmap)

A subset of this, is address space allocated by the program (via malloc)

...and then there is memory actually in use, which is an entirely different
thing, of which we currently only have some kind of clue in the VM

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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