Re: [Qemu-devel] [PATCH 07/15] qapi: use mmap for QmpInputVisitor

[Paolo Bonzini]

On 04/07/2016 13:18, Markus Armbruster wrote:
> Paolo Bonzini <address@hidden> writes:
> 
>> On 30/06/2016 16:12, Markus Armbruster wrote:
>>> Implementing a stack as "big enough" array can be wasteful.
>>> Implementing it as dynamically allocated list is differently wasteful.
>>> Saving several mallocs and frees can be worth "wasting" a few pages of
>>> memory for a short time.
>>
>> Most usage of QmpInputVisitor at startup comes from
>> object_property_set_qobject, which only sets small scalar objects.  The
>> stack is entirely unused in this case.
> 
> A quick test run shows ~300 qmp_input_visitor_new() calls during
> startup, with at most two alive at the same time.
> 
> Why would it matter whether these are in the order of 150 bytes or 25000
> bytes each?  How could this materially impact RSS?

I think we agree that it doesn't.  The question in the subthread is
whether we can improve QmpInputVisitor in general.

Paolo