[haiku-development] Re: Out of memory errors when virtual memory disabled
- From: "Ingo Weinhold" <ingo_weinhold@xxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Mon, 05 Dec 2011 21:05:01 +0100
Adrien Destugues wrote:
> Le 05/12/2011 16:09, Rene Gollent a écrit :
> > On Mon, Dec 5, 2011 at 10:08 AM, Rimas Kudelis<rq@xxxxxx> wrote:
> >> ah, I see... I had no idea that on fork(), a child process gets the same
> >> amount of memory as its parent by default...
> > It more or less has to, since the child is an exact clone of the
> > parent by fork() semantics.
>
> Don't we have some lazy copy-on-write thing there ?
We do. But, as Rene explained, there's a difference between committing and
allocated memory. When CoW'ing a writable area the system does not allocate
twice the memory, but it does commit that much. Again, allocating memory means
actually using physical pages (or slots in the swap file). Committing memory
means, that the system ensures that that much memory can be allocated, if
requested, but until then it can be used otherwise (e.g. for caching) or lies
dormant (swap space). Committing memory on CoW is necessary, since writing to
that area will cause memory allocations, which could otherwise fail and thus
crash the program.
CU, Ingo
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