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

[Gioh Kim <gioh.kim@lge.com>]

2015-07-08 오전 7:37에 Andrew Morton 이(가) 쓴 글:
> On Tue,  7 Jul 2015 13:36:20 +0900 Gioh Kim <gioh.kim@lge.com> wrote:
>
>> From: Gioh Kim <gurugio@hanmail.net>
>>
>> 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.


>
> Why are your changes to the GPU driver not included in this patch series?

My platform is ARM-based and GPU is ARM-Mali. The driver is not open source.
It's too bad that I cannot show effect of this patch with the GPU driver.


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