Re: Suspicious error for CMA stress test

Joonsoo Kim
2016-03-04T02:09:09Z

On Thu, Mar 03, 2016 at 10:52:17AM -0800, Laura Abbott wrote:
> On 03/03/2016 04:49 AM, Hanjun Guo wrote:
> >On 2016/3/3 15:42, Joonsoo Kim wrote:
> >>2016-03-03 10:25 GMT+09:00 Laura Abbott <labbott@redhat.com>:
> >>>(cc -mm and Joonsoo Kim)
> >>>
> >>>
> >>>On 03/02/2016 05:52 AM, Hanjun Guo wrote:
> >>>>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
> >[...]
> >>>
> >>>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.