Number of components per init

[Norman Feske]

Hi Roman,

> I agree. Making the preservation configurable makes the memory 
> reservations more transparent, i.e. everything that requires memory is 
> visible in init's configuration - well, at least if init is used in a 
> static way. Or are there still other memory 'pools' one might not be 
> aware of?

on NOVA, the most important one is the kernel's memory pool, which has a
fixed size that is defined in the kernel's linker script. The linker
script is located in nova/src/hypervisor.ld (look for '_mempool_f').

Another limited resource is core's capability space, in particular the
meta data required to manage the lifetime of capabilities. The details
differ from kernel to kernel. On most base platforms, those information
are kept in statically allocated arrays, which are dimensioned to
accommodate the current scenarios. Core is in a special position because
it has to keep track of all capabilities in the system (capabilities are
allocated via core's PD service). Since the capability space of core is
limited, we should apply Genode's resource-trading concept to
capabilities too. In fact, I plan to implement this idea sometime next
year. Until then, we have to life with the situation that capability
allocations are not properly accounted (which is a potential
denial-of-service issue).

> One last question: how do I calculate the required memory preservation 
> for init on nova_x86_64, based on the number of children?

I cannot give you a precise formula. My previously reported experiment
where I started over 70 children with the default preservation of 128
KiB suggests that 2 KiB per child should suffice. Make it 16 KiB per
child and you should be really fine. ;-)

Cheers
Norman

-- 
Dr.-Ing. Norman Feske
Genode Labs

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