Re: [PATCH 1/4] workqueue:Fix unbound workqueue's node affinity detection

[Lai Jiangshan]

On 12/16/2014 03:32 PM, Kamezawa Hiroyuki wrote:
> (2014/12/16 14:30), Lai Jiangshan wrote:
>> On 12/15/2014 07:14 PM, Kamezawa Hiroyuki wrote:
>>> Unbound wq pool's node attribute is calculated at its allocation.
>>> But it's now calculated based on possible cpu<->node information
>>> which can be wrong after cpu hotplug/unplug.
>>>
>>> If wrong pool->node is set, following allocation error will happen.
>>> ==
>>>   SLUB: Unable to allocate memory on node 2 (gfp=0x80d0)
>>>    cache: kmalloc-192, object size: 192, buffer size: 192, default order:
>>> 1, min order: 0
>>>    node 0: slabs: 6172, objs: 259224, free: 245741
>>>    node 1: slabs: 3261, objs: 136962, free: 127656
>>> ==
>>>
>>> This patch fixes the node detection by making use of online cpu info.
>>> Unlike cpumask, the best node can be calculated by degree of overlap
>>> between attr->cpumask and numanode->online_cpumask.
>>> This change doesn't corrupt original purpose of the old calculation.
>>>
>>> Note: it's expected that this function is called as
>>>        pool_detect_best_node
>>>        get_unbound_pool
>>>        alloc_unbound_pwq
>>>        wq_update_unbound_numa
>>>        called at CPU_ONLINE/CPU_DOWN_PREPARE
>>> and the latest online cpu info can be applied to a new wq pool,
>>> which replaces old one.
>>>
>>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>>> ---
>>>   kernel/workqueue.c | 38 ++++++++++++++++++++++++++------------
>>>   1 file changed, 26 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>>> index 09b685d..7809154 100644
>>> --- a/kernel/workqueue.c
>>> +++ b/kernel/workqueue.c
>>> @@ -3440,6 +3440,31 @@ static void put_unbound_pool(struct worker_pool *pool)
>>>   }
>>>
>>>   /**
>>> + * pool_detect_best_node - detect a node which contains specified cpumask.
>>> + * Should be called with wq_pool_mutex held.
>>> + * Returns a online node where the most of given cpus are tied to.
>>> + */
>>> +static int pool_detect_best_node(const struct cpumask *cpumask)
>>> +{
>>> +    int node, best, match, selected = NUMA_NO_NODE;
>>> +    static struct cpumask andmask; /* under wq_pool_mutex */
>>> +
>>> +    if (!wq_numa_enabled ||
>>> +        cpumask_subset(cpu_online_mask, cpumask))
>>> +        goto out;
>>> +    best = 0;
>>> +    /* select a node which contains the most number of cpu */
>>> +    for_each_node_state(node, N_ONLINE) {
>>> +        cpumask_and(&andmask, cpumask, cpumask_of_node(node));
>>> +        match = cpumask_weight(&andmask);
>>> +        if (match > best)
>>> +            selected = best;
>>> +    }
>>> +out:
>>> +    return selected;
>>> +}
>>
>>
>> This is a mixture of fix and development.  Why not just keep the original calculation?
>>
> Just because wq_numa_possible_mask is broken, 

It is not broken if the bug is fixed.

> it shouldn't be used if possible.
> In this patch series, the mask is updated only when a node is coming up.
> Is it better to clear it at node offline ?
> 
>> if the mask cover multiple nodes, NUMA_NO_NODE is the best for pool->node
>> after the pool was created. The memory allocation will select the best node
>> for manage_workers(), from which CPU that the worker actually is running on.
>>
> 
> I'll drop this and try to keep original code as much as possible.
> 
> Thanks,
> -Kame
> 
> 
> .
> 

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