Re: [Xen-devel] [PATCH v5 4/8] mm: Scrub memory from idle loop

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> 07/23/17 4:14 AM >>>
>>> @@ -1050,17 +1120,42 @@ static void scrub_free_pages(unsigned int node)
>>> -                if ( node_need_scrub[node] == 0 )
>>> -                    return;
>>> +                if ( preempt || (node_need_scrub[node] == 0) )
>>> +                    goto out;
>>>               }
>>>           } while ( order-- != 0 );
>>>       }
>>> +
>>> + out:
>>> +    spin_unlock(&heap_lock);
>>> +    node_clear(node, node_scrubbing);
>>> +    return softirq_pending(cpu) || (node_to_scrub(false) != NUMA_NO_NODE);
>> 
>> While I can see why you use it here, the softirq_pending() looks sort of
>> misplaced: While invoking it twice in the caller will look a little odd too,
>> I still think that's where the check belongs.
>
>
>scrub_free_pages is called from idle loop as
>
>else if ( !softirq_pending(cpu) && !scrub_free_pages() )
>pm_idle();
>
>so softirq_pending() is unnecessary here.
>
>(Not sure why you are saying it would be invoked twice)

That was sort of implicit - the caller would want to become


    else if ( !softirq_pending(cpu) && !scrub_free_pages() && 
!softirq_pending(cpu) )
    pm_idle();

to account for the fact that a softirq may become pending while scrubbing.

Jan


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