On Thu, Mar 03, 2016 at 10:52:17AM -0800, Laura Abbott wrote:

On 03/03/2016 04:49 AM, Hanjun Guo wrote:

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On 2016/3/3 15:42, Joonsoo Kim wrote:

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2016-03-03 10:25 GMT+09:00 Laura Abbott [off-list ref]:

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(cc -mm and Joonsoo Kim)


On 03/02/2016 05:52 AM, Hanjun Guo wrote:

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Hi,

I came across a suspicious error for CMA stress test:

Before the test, I got:
-bash-4.3# cat /proc/meminfo | grep Cma
CmaTotal:         204800 kB
CmaFree:          195044 kB


After running the test:
-bash-4.3# cat /proc/meminfo | grep Cma
CmaTotal:         204800 kB
CmaFree:         6602584 kB

So the freed CMA memory is more than total..

Also the the MemFree is more than mem total:

-bash-4.3# cat /proc/meminfo
MemTotal:       16342016 kB
MemFree:        22367268 kB
MemAvailable:   22370528 kB

[...]

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I played with this a bit and can see the same problem. The sanity
check of CmaFree < CmaTotal generally triggers in
__move_zone_freepage_state in unset_migratetype_isolate.
This also seems to be present as far back as v4.0 which was the
first version to have the updated accounting from Joonsoo.
Were there known limitations with the new freepage accounting,
Joonsoo?

I don't know. I also played with this and looks like there is
accounting problem, however, for my case, number of free page is slightly less
than total. I will take a look.

Hanjun, could you tell me your malloc_size? I tested with 1 and it doesn't
look like your case.

I tested with malloc_size with 2M, and it grows much bigger than 1M, also I
did some other test:

 - run with single thread with 100000 times, everything is fine.

 - I hack the cam_alloc() and free as below [1] to see if it's lock issue, with
   the same test with 100 multi-thread, then I got:

-bash-4.3# cat /proc/meminfo | grep Cma
CmaTotal: 204800 kB
CmaFree: 225112 kB

It only increased about 30M for free, not 6G+ in previous test, although
the problem is not solved, the problem is less serious, is it a synchronization
problem?

'only' 30M is still an issue although I think you are right about something related
to synchronization. When I put the cma_mutex around free_contig_range I don't see

Hmm... I can see the issue even if putting the cma_mutex around
free_contig_range().

In other reply, I attached the code to temporary close the race.

the issue. I wonder if free of the pages is racing with the undo_isolate_page_range
on overlapping ranges caused by outer_start?

I don't know yet.
Anyway, it looks like that the problem that I want to fix by commit '3c60509'
still remains.

Thanks.