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List:       linux-mm
Subject:    Re: [RFC][PATCH] migrate_pages:skip migration between intersect
From:       Christoph Lameter <cl () linux-foundation ! org>
Date:       2010-03-31 14:17:30
Message-ID: alpine.DEB.2.00.1003310914290.17298 () router ! home
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On Wed, 31 Mar 2010, Bob Liu wrote:

> > The intended semantic is the preservation of the relative position of the
> > page to the beginning of the node set. If you do not want to preserve the
> > relative position then just move portions of the nodes around.
> >
>
> Hmm.,
> Sorry I still haven't understand your mention :-)
>
> My concern was why move the pages in the intersect nodes.I think skipping
> this migration we can also satisfy the user's request.
> In the above semantic, I  haven't got the result.

No skipping does *not* satisfy the users request since the relative
position of the page from the beginning of the nodesset is not
preserved.

You end up with a mess without this requirement. F.e. if you use page
migration (or cpuset automigration) to shift an application running on 10
nodes up by two nodes to make a hole that would allow you to run another
application on the lower nodes. Applications place pages intentionally on
certain nodes to be able to manage memory distances.

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