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

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Date:	Mon, 13 May 2013 10:19:02 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	Minchan Kim <minchan@...nel.org>,
	Lin Feng <linfeng@...fujitsu.com>, akpm@...ux-foundation.org,
	bcrl@...ck.org, viro@...iv.linux.org.uk, khlebnikov@...nvz.org,
	walken@...gle.com, kamezawa.hiroyu@...fujitsu.com, riel@...hat.com,
	rientjes@...gle.com, isimatu.yasuaki@...fujitsu.com,
	wency@...fujitsu.com, laijs@...fujitsu.com, jiang.liu@...wei.com,
	zab@...hat.com, jmoyer@...hat.com, linux-mm@...ck.org,
	linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH V2 1/2] mm: hotplug: implement non-movable version of
 get_user_pages() called get_user_pages_non_movable()

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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