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

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

> 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.
>>
>
> In a glance, ss Konstantin pointed out this set, while it twists chunks around,
> brings back code we got rid of a while ago because it was messy and racy.

Yes, your point is right.

> I'll take a closer look into your work next week, but for now, I'd say
> we should not follow this patch of reintroducing long-dead code.

BUT as I replied to Konstantin, the code for balloon driver is to show
how the generic callbacks can be applied.

My point is there are some pages to be migrated which are not LRU pages,
but there is no interface for them to migrate.

For example gpu driver has many, not mapped to kernel space, pages.
Those pages can be migrated when GPU is not working, screen is not refreshed.
And zram pages can be migrated also.

I'm very sorry that I'm not familiar to balloon driver.
If you give me some hints, I might be able to refine code of patch 2~3 in the next spin.

Thank you for the feedback.

>
> Cheers!
> -- Rafael
>
>>
>> Gioh Kim (4):
>>    mm/compaction: enable driver page migration
>>    mm/balloon: apply migratable-page into balloon driver
>>    mm/compaction: apply migratable-page into compaction
>>    mm: remove direct migration of migratable-page
>>
>>   drivers/virtio/virtio_balloon.c        |  2 +
>>   fs/proc/page.c                         |  4 +-
>>   include/linux/balloon_compaction.h     | 42 +++++++++++++++------
>>   include/linux/compaction.h             | 13 +++++++
>>   include/linux/fs.h                     |  2 +
>>   include/linux/mm.h                     | 14 +++----
>>   include/linux/pagemap.h                | 27 ++++++++++++++
>>   include/uapi/linux/kernel-page-flags.h |  2 +-
>>   mm/balloon_compaction.c                | 67 +++++++++++++++++++++++++++++-----
>>   mm/compaction.c                        |  9 +++--
>>   mm/migrate.c                           | 25 ++++---------
>>   11 files changed, 154 insertions(+), 53 deletions(-)
>>
>> --
>> 1.9.1
>>
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>