Re: [PATCH V2 1/2] mm: hotplug: implement non-movable version ofget_user_pages() called get_user_pages_non_movable()

From: Tang Chen
Date: Mon May 13 2013 - 05:08:57 EST


Hi Mel,

On 02/06/2013 05:56 PM, Mel Gorman wrote:

There is the possibility that callbacks could be introduced for
migrate_unpin() and migrate_pin() that takes a list of PFN pairs
(old,new). The unpin callback should release the old PFNs and barrier
against any operations until the migrate_pfn() callback is called with
the updated pfns to be repinned. Again it would fully depend on subsystems
implementing it properly.

The callback interface would be more robust but puts a lot more work on
the driver side where your milage will vary.


I'm very interested in the "callback" way you said.

For memory hot-remove case, the aio pages are pined in memory and making
the pages cannot be offlined, furthermore, the pages cannot be removed.

IIUC, you mean implement migrate_unpin() and migrate_pin() callbacks in aio
subsystem, and call them when hot-remove code tries to offline pages, right ?

If so, I'm wondering where should we put this callback pointers ?
In struct page ?


It has been a long time since this topic was discussed. But to solve this
problem cleanly for hotplug guys and CMA guys, please give some more comments.

Thanks. :)


To guarantee CMA can migrate pages pinned by drivers I think you need
migrate-related callsbacks to unpin, barrier the driver until migration
completes and repin.

I do not know, or at least have no heard, of anyone working on such a
scheme.

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