Re: [RFCv2] mm: page allocation for less fragmentation

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

2015-03-26 i??i ? 7:16i?? Vlastimil Babka i?'(e??) i?' e,?:
> On 25.3.2015 3:39, Gioh Kim wrote:
>> My driver allocates more than 40MB pages via alloc_page() at a time and
>> maps them at virtual address. Totally it uses 300~400MB pages.
>>
>> If I run a heavy load test for a few days in 1GB memory system, I cannot allocate even order=3 pages
>> because-of the external fragmentation.
>>
>> I thought I needed a anti-fragmentation solution for my driver.
>> But there is no allocation function that considers fragmentation.
>> The compaction is not helpful because it is only for movable pages, not unmovable pages.
>>
>> This patch proposes a allocation function allocates only pages in the same pageblock.
>>
>> I tested this patch like following:
>>
>> 1. When the driver allocates about 400MB and do "cat /proc/pagetypeinfo;cat /proc/buddyinfo"
>>
>> Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
>> Node    0, zone   Normal, type    Unmovable   3864    728    394    216    129     47     18      9      1      0      0
>> Node    0, zone   Normal, type  Reclaimable    902     96     68     17      3      0      1      0      0      0      0
>> Node    0, zone   Normal, type      Movable   5146    663    178     91     43     16      4      0      0      0      0
>> Node    0, zone   Normal, type      Reserve      1      4      6      6      2      1      1      1      0      1      1
>> Node    0, zone   Normal, type          CMA      0      0      0      0      0      0      0      0      0      0      0
>> Node    0, zone   Normal, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
>>
>> Number of blocks type     Unmovable  Reclaimable      Movable      Reserve          CMA      Isolate
>> Node 0, zone   Normal          135            3          124            2            0            0
>> Node 0, zone   Normal   9880   1489    647    332    177     64     24     10      1      1      1
>>
>> 2. The driver frees all pages and allocates pages again with alloc_pages_compact.
>
> This is not a good test setup. You shouldn't switch the allocation types during
> single system boot. You should compare results from a boot where common
> allocation is used and from a boot where your new allocation is used.

The new allocator is slower so I don't think it can replace current allocator.
I don't aim to change general allocator.
The main pupose of the new allocator is a specific allocator if system has too much fragmentation.
If some drivers consume much memory and generate fragmentation, it can use new allocator instead at the time.
I want to make a kind of compaction for drivers that allocates unmovable pages.

Therefore I tested like that.
I first generated fragmentation and called the new allocator.
I wanted to check whether the fragmentation was caused by my driver
and the pages of the driver was able to be compacted.
I thought the pages was compacted.

If I freed pages and called the commmon allocator again,
it could decrease a little fragmentation (not much as the new allocator).
But there was no pages compaction and fragmentation would increase soon.


>
>> This is a kind of compaction of the driver.
>> Following is the result of "cat /proc/pagetypeinfo;cat /proc/buddyinfo"
>>
>> Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
>> Node    0, zone   Normal, type    Unmovable      8      5      1    432    272     91     37     11      1      0      0
>> Node    0, zone   Normal, type  Reclaimable    901     96     68     17      3      0      1      0      0      0      0
>> Node    0, zone   Normal, type      Movable   4790    776    192     91     43     16      4      0      0      0      0
>> Node    0, zone   Normal, type      Reserve      1      4      6      6      2      1      1      1      0      1      1
>> Node    0, zone   Normal, type          CMA      0      0      0      0      0      0      0      0      0      0      0
>> Node    0, zone   Normal, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
>>
>> Number of blocks type     Unmovable  Reclaimable      Movable      Reserve          CMA      Isolate
>> Node 0, zone   Normal          135            3          124            2            0            0
>> Node 0, zone   Normal   5693    877    266    544    320    108     43     12      1      1      1
>
> The number of unmovable pageblocks didn't change here. The stats for free
> unmovable pages does look better for higher orders than in the first listing
> above, but even the common allocation logic would give you that result, if you
> allocated your 400 MB using (many) order-0 allocations (since you apparently
> don't care about physically contiguous memory). That would also prefer order-0
> free pages before splitting higher orders. So this doesn't demonstrate benefits
> of the alloc_pages_compact() approach I'm afraid. The results suggest that the
> system was in a worst state when the first allocation happened, and meanwhile
> some pages were freed, creating the large numbers of order-0 unmovable free
> pages. Or maybe the system got fragmented in the first allocation because your
> driver tries to allocate the memory with high-order allocations before falling
> back to lower orders? That would probably defeat the natural anti-fragmentation
> of the buddy system.

My driver is allocating pages only with alloc_page, not alloc_pages with high order.

Yes, if I freed pages and called alloc_page again, it could decrease fragmentation at the time.
But there was no compaction and fragmentation would increase soon,
because the allocated pages was scattered all over the system.

The new allocator compacts pages. I believe it can decrease fragmentation for long time.

>
> So a proper test could be based on this:
>
>> If I run a heavy load test for a few days in 1GB memory system, I cannot
> allocate even order=3 pages
>> because-of the external fragmentation.
>
> With this patch, is the situation quantifiably better? Can you post the
> pagetype/buddyinfo for system boot where all driver allocations use the common
> allocator, and system boot with the patch? That should be comparable if the
> workload is the same for both boots.
>

OK. I'll. I can be good test.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>