Re: [Qemu-devel] [RFC PATCH] Convert ram_list to RCU DQ V2

[Paolo Bonzini]

Il 03/09/2013 15:56, Mike Day ha scritto:
>> > +    /* this implements a long-running RCU critical section.
>> > +     * When rcu reclaims in the code start to become numerous
>> > +     * it will be necessary to reduce the granularity of this critical
>> > +     * section.
>> > +     */
>>
>> Please add the same comment (and a rcu_read_lock/unlock pair replacing
>> the ramlist mutex) in ram_save_iterate, too.
> 
> Just double checking on this particular change. In practice ram_save
> manipulates the ram_list indirectly through ram_save_block. But I'm
> assuming you want this change because of the ram state info that
> persists between calls to ram_save (ram_list version in particular).

ram_list.version is not really a problem, but last_seen_block has to
persist across ram_save_block calls.

> Also, there is potential for the callback functions
> ram_control_*_iterate to manipulate the ram_list.

I think that's right now not possible (and they could use
rcu_read_lock/unlock as well).

Paolo