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@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.
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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