Re: [BUG REPORT] [mm-hotplug, aio] aio ring_pages can't be offlined

[Lin Feng <linfeng@cn.fujitsu.com>]

hi Andrew,

On 11/30/2012 07:39 AM, Andrew Morton wrote:
> Tricky.
> 
> I expect the same problem would occur with pages which are under
> O_DIRECT I/O.  Obviously O_DIRECT pages won't be pinned for such long
> periods, but the durations could still be lengthy (seconds).
the offline retry timeout duration is 2 minutes, so to O_DIRECT pages 
seem maybe not a problem for the moment.
> 
> Worse is a futex page, which could easily remain pinned indefinitely.
> 
> The best I can think of is to make changes in or around
> get_user_pages(), to steal the pages from userspace and replace them
> with non-movable ones before pinning them.  The performance cost of
> something like this would surely be unacceptable for direct-io, but
> maybe OK for the aio ring and futexes.
thanks for your advice.
I want to limit the impact as little as possible, as mentioned above,
direct-io seems not a problem, we needn't touch them. Maybe we can 
just change the use of get_user_pages()(in or around) such as aio 
ring pages. I will try to find a way to do this.

Thanks,
linfeng