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

[Mel Gorman <mgorman@suse.de>]

On Mon, May 13, 2013 at 05:11:43PM +0800, Tang Chen wrote:
> 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 ?
> 

No, I would expect the callbacks to be part the address space operations
which can be found via page->mapping.

-- 
Mel Gorman
SUSE Labs

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