Re: RFC -- new zone type

[Larry Bassel <lbassel@codeaurora.org>]

On 29 Sep 11 13:19, Andi Kleen wrote:
> Larry Bassel <lbassel@codeaurora.org> writes:
> >
> > It was suggested to me that a new zone type which would be similar
> > to the "movable zone" but is only allowed to contain pages
> > that can be discarded (such as text) could solve this problem,
> 
> This may not actually be a win because if the text pages are needed
> afterwards the act of rereading them from disk would likely take longer
> than the copying.

Yes, I'm aware of this (they'd actually be coming from flash
which is even slower, right?).

> 
> The so you many not get latency before, but after.
> 
> Essentially robbing Peter to pay Paul.

Yes, the goal is to create this large contiguous memory
quickly, even if performance is worse later on for a while.

> 
> If the goal is to just spread the latency over a longer time
> I'm sure there are better ways to do that than to add a new zone.

I myself am not an advocate of creating this new zone (because
I think there may not be a lot of benefit to it for the
amount of work involved), but I want to solicit people's
opinions about it and collect suggestions (such as Dan's)
about alternate approaches that may be better/closer
to already implemented (I'd likely have to port them
to ARM as they probably were developed for x86, but I don't
think that's a problem) that will handle our use case.

I wonder if another reasonable approach might be a combination
of memory compaction in the background when the machine
is otherwise idle, combined with occasional killing of
processes that haven't been used for a long time (this is
going to be run on an android user environment, android
likes to leave lots of unused processes running in the
background).

> 
> -Andi

Larry

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