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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Message-ID: <5191926A.2090608@cn.fujitsu.com>
Date:	Tue, 14 May 2013 09:24:58 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Benjamin LaHaise <bcrl@...ck.org>, Jeff Moyer <jmoyer@...hat.com>,
	Mel Gorman <mgorman@...e.de>
CC:	Minchan Kim <minchan@...nel.org>,
	Lin Feng <linfeng@...fujitsu.com>, akpm@...ux-foundation.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, 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()

Hi Mel, Benjamin, Jeff,

On 05/13/2013 11:01 PM, Benjamin LaHaise wrote:
> On Mon, May 13, 2013 at 10:54:03AM -0400, Jeff Moyer wrote:
>> How do you propose to move the ring pages?
>
> It's the same problem as doing a TLB shootdown: flush the old pages from
> userspace's mapping, copy any existing data to the new pages, then
> repopulate the page tables.  It will likely require the addition of
> address_space_operations for the mapping, but that's not too hard to do.
>

I think we add migrate_unpin() callback to decrease page->count if 
necessary,
and migrate the page to a new page, and add migrate_pin() callback to pin
the new page again.

The migrate procedure will work just as before. We use callbacks to 
decrease
the page->count before migration starts, and increase it when the migration
is done.

And migrate_pin() and migrate_unpin() callbacks will be added to
struct address_space_operations.

Is that right ?

If so, I'll be working on it.

Thanks. :)
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