Number of components per init

Roman Iten roman.iten at ...453...
Wed Oct 5 16:48:18 CEST 2016

Hi Norman

>>  - How big is the initial quota of init?
> init receives the quota for all the available physical memory from 
> core.
> The amount depends on the physical memory of the machine. It is 
> printed
> by core when init is started.

Thats what I thought. But I couldn't imagine how init's quota could 
possibly exceed on a x86-64 machine with several GiB physical memory :)

> For each child started by init, init needs to create several
> capabilities (e.g., the parent capability presented to the child, or 
> the
> capability for the local ROM session for providing the child's binary 
> as
> "binary" ROM module). The allocation of those capabilities is 
> performed
> via the 'Nova_native_pd::alloc_rpc_cap' RPC function. This function
> naturally consumes session quota of the corresponding PD session 
> (init's
> PD session). At one point, the initial session quota (that was passed 
> to
> core when init's PD session was created) is depleted. In this case, 
> core
> prints the diagnostic message and returns an error to the client 
> (init).
> Init responds to this error by upgrading the session quota of its PD
> session using the preserved slack memory. The session upgrading is
> handled at 'base-nova/src/lib/base/'.

> In your case, the message you see is merely a diagnostic message. The
> condition is handled properly. In cases where proper error handing of
> the 'Out_of_metadata' condition is missing, the message used to be 
> quite
> valuable to spot the problem. So we decided to kept it.

How can I distinguish if the condition is handled properly or not? Are 
there any preceding or following log messages in either case?

>>  - Does the size of the metadata allocation for a child depends on
>>  whether I'm using a 32 or 64 bit system?
> Yes. I.e., your scenario produces the message only on 64 bit, not on 
> 32 bit.

Is it worth thinking about calculating the slack memory size based on 
Genode::addr_t? Or make the value even configurable?

> That said, the limit turned out not to be a problem in your case. The
> message is a false-positive warning. The default limit becomes a 
> problem
> not before the PD-session upgrade fails. I can trigger the problem 
> with
> your run script when configuring Qemu with 64 MiB of memory and 
> starting
> 76 children. Sorry that my previous email pointed you to the wrong
> direction.

It didn't. I'm trying to improve my understanding of memory 
configuration and allocation in Genode. So every hint helps ;)

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