On Tue, May 14, 2013 at 09:24:58AM +0800, Tang Chen wrote:
> 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.
You can't just decrease the page count for this to work. The pages are
pinned because aio_complete() can occur at any time and needs to have a
place to write the completion events. When changing pages, aio has to
take the appropriate lock when changing one page for another.
> 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.
I think the existing migratepage operation in address_space_operations can
be used. Does it get called when hot unplug occurs? That is: is testing
with the migrate_pages syscall similar enough to the memory removal case?
-ben
> Is that right ?
>
> If so, I'll be working on it.
>
> Thanks. :)
--
"Thought is the essence of where you are now."
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