On Thu, Aug 26, 2010 at 7:06 PM, Peter Zijlstra [off-list ref] wrote:

On Thu, 2010-08-26 at 18:29 +0900, Minchan Kim wrote:

quoted

As I said following mail, I said about free space problem.
Of course, compaction could move anon pages into somewhere.
What's is somewhere? At last, it's same zone.
It can prevent fragment problem but not size of free space.
So I mean it would be better to move it into another zone(ex, HIGHMEM)
rather than OOM kill.

Real machines don't have highmem, highmem sucks!! /me runs

It's another topic.
I agree highmem isn't a gorgeous. But my desktop isn't real machine?
Important thing is that we already have a highmem and many guys
include you(kmap stacking patch :))try to improve highmem problems. :)

Does cross zone movement really matter, I though these crappy devices
were mostly used on crappy hardware with very limited memory, so pretty
much everything would be in zone_normal.. no?

No. Until now, many embedded devices have used to small memory. In
that case, only there is a DMA zone in system. But as I know, mobile
phone starts to use big(?) memory like 1G or above sooner or later. So
they starts to use HIGHMEM. Otherwise, 2G/2G space configuration.
Some embedded device uses many thread model to port easily from RTOS.
In that case, they don't have enough address space for application if
it uses 2G/2G model.

So we should care of HIGHMEM in embedded system from now on.

But sure, if there's really a need we can look at maybe doing cross zone
movement.

-- 
Kind regards,
Minchan Kim