Re: [RFCv3 0/5] enable migration of driver pages

[Minchan Kim]

On Wed, Jul 08, 2015 at 09:19:50AM +0900, Gioh Kim wrote:
> 
> 
> 2015-07-08 ìì 9:07ì Andrew Morton ì(ê) ì ê:
> >On Wed, 08 Jul 2015 09:02:59 +0900 Gioh Kim <gioh.kim@xxxxxxx> wrote:
> >
> >>
> >>
> >>2015-07-08 ______ 7:37___ Andrew Morton ___(___) ___ ___:
> >>>On Tue,  7 Jul 2015 13:36:20 +0900 Gioh Kim <gioh.kim@xxxxxxx> wrote:
> >>>
> >>>>From: Gioh Kim <gurugio@xxxxxxxxxxx>
> >>>>
> >>>>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.
> >>>>
> >>>>...
> >>>>
> >>>>This patch set is tested:
> >>>>- 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
> >>>
> >>>OK, but what happens if the balloon driver is not used to force
> >>>compaction?  Does your test machine successfully compact pages on
> >>>demand, so those order-3 allocations now succeed?
> >>
> >>If any driver that has many pages like the balloon driver is forced to compact,
> >>the system can get free high-order pages.
> >>
> >>I have to show how this patch work with a driver existing in the kernel source,
> >>for kernel developers' undestanding. So I selected the balloon driver
> >>because it has already compaction and working with kernel compaction.
> >>I can show how driver pages is compacted with lru-pages together.
> >>
> >>Actually balloon driver is not best example to show how this patch compacts pages.
> >>The balloon driver compaction is decreasing page consumtion, for instance 1024MB -> 512MB.
> >>I think it is not compaction precisely. It frees pages.
> >>Of course there will be many high-order pages after 512MB is freed.
> >
> >Can the various in-kernel GPU drivers benefit from this?  If so, wiring
> >up one or more of those would be helpful?
> 
> I'm sure that other in-kernel GPU drivers can have benefit.
> It must be helpful.
> 
> If I was familiar with other in-kernel GPU drivers code, I tried to patch them.
> It's too bad.
> 
> Minchan Kim said he had a plan to apply this patch into zram compaction.
> Many embedded machines use several hundreds MB for zram.
> The zram can also have benefit with this patch as much as GPU drivers.
> 

Hello Gioh,

It would be helpful for fork-latency and zra+CMA in small memory system.
I will implement zsmalloc.migratepages after I finish current going works.

Thanks for the nice work!

-- 
Kind regards,
Minchan Kim
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