Re: [PATCH -mm] do_migrate_pages() calls migrate_to_node() even iftask is already on a correct node

[Larry Woodman]

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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