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SubjectRe: [PATCH -mm] do_migrate_pages() calls migrate_to_node() even if task is already on a correct node
On 03/29/2012 03:43 PM, KOSAKI Motohiro wrote:
> (3/29/12 2:00 PM), Larry Woodman wrote:
>> On 03/22/2012 03:30 PM, Christoph Lameter wrote:
>>> On Thu, 22 Mar 2012, Larry Woodman wrote:
>>>
>>>>> Application may manage their locality given a range of nodes and
>>>>> each of
>>>>> the x .. x+n nodes has their particular purpose.
>>>> So to be clear on this, in that case the intention would be move 3
>>>> to 4, 4 to
>>>> 5 and 5 to 6
>>>> to keep the node ordering the same?
>>> Yup. Have a look at do_migrate_pages and the descrition in the
>>> comment by
>>> there by Paul Jackson.
>>>
>>>
>> Christoph and others what do you think about this???
>>
>>
>> for_each_node_mask(s, tmp) {
>> +
>> + /* IFF there is an equal number of source and
>> + * destination nodes, maintain relative node distance
>> + * even when source and destination nodes overlap.
>> + * However, when the node weight is unequal, never move
>> + * memory out of any destination nodes */
>> + if ((nodes_weight(*from_nodes) !=
>> nodes_weight(*to_nodes)) &&
>> + (node_isset(s, *to_nodes)))
>> + continue;
>> +
>> d = node_remap(s, *from_nodes, *to_nodes);
>> if (s == d)
>> continue;
>
> I'm confused. Could you please explain why you choose nodes_weight()?
> On my first impression,
> it seems almostly unrelated factor.

nodes_weight() tells us the number of nodes in the cpuset so if you are
migrating
from say 2, 3 &4 to 3, 4 &5 we wont go from 2 to 5 and call it done like
the original
patch did. With this patch we will preserve the migrating of 2, 3 &4 to
3, 4 &5 yet
if we are migrating from 0-7 to 3-4 we wont do this:

Migrating 7 to 4
Migrating 6 to 3
Migrating 5 to 4
Migrating 4 to 3
Migrating 1 to 4
Migrating 3 to 4
Migrating 0 to 3
Migrating 2 to 3

Instead, will do this:

Migrating 7 to 4
Migrating 6 to 3
Migrating 5 to 4
Migrating 1 to 4
Migrating 0 to 3
Migrating 2 to 3

Larry

>
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