Re: [RFC 0/4] enable migration of non-LRU pages

[Gioh Kim]

2015-06-10 ìì 9:08ì Minchan Kim ì(ê) ì ê:
> Hello Gioh,
>
> On Tue, Jun 02, 2015 at 04:27:40PM +0900, Gioh Kim wrote:
> > Hello,
> >
> > This series try to enable migration of non-LRU pages, such as driver's page.
> >
> > My ARM-based platform occured severe fragmentation problem after long-term
> > (several days) test. Sometimes even order-3 page allocation failed. It has
> > memory size 512MB ~ 1024MB. 30% ~ 40% memory is consumed for graphic processing
> > and 20~30 memory is reserved for zram.
> >
> > I found that many pages of GPU driver and zram are non-movable pages. So I
> > reported Minchan Kim, the maintainer of zram, and he made the internal
> > compaction logic of zram. And I made the internal compaction of GPU driver.
> >
> > They reduced some fragmentation but they are not enough effective.
> > They are activated by its own interface, /sys, so they are not cooperative
> > with kernel compaction. If there is too much fragmentation and kernel starts
> > to compaction, zram and GPU driver cannot work with the kernel compaction.
> >
> > The first this patch adds a generic isolate/migrate/putback callbacks for page
> > address-space. The zram and GPU, and any other modules can register
> > its own migration method. The kernel compaction can call the registered
> > migration when it works. Therefore all page in the system can be migrated
> > at once.
> >
> > The 2nd the generic migration callbacks are applied into balloon driver.
> > My gpu driver code is not open so I apply generic migration into balloon
> > to show how it works. I've tested it with qemu enabled by kvm like followings:
> > - turn on Ubuntu 14.04 with 1G memory on qemu.
> > - do kernel building
> > - after several seconds check more than 512MB is used with free command
> > - command "balloon 512" in qemu monitor
> > - check hundreds MB of pages are migrated
> >
> > Next kernel compaction code can call generic migration callbacks instead of
> > balloon driver interface.
> > Finally calling migration of balloon driver is removed.
>
> I didn't hava a time to review but it surely will help using zram with
> CMA as well as fragmentation of the system memory via making zram objects
> movable.

I know you are busy. I hope you make time for review.

> If it lands on mainline, I will work for zram object migration.
>
> Thanks!
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