Re: Suspicious error for CMA stress test

[Hanjun Guo]

On 03/07/2016 04:16 PM, Leizhen (ThunderTown) wrote:
> On 2016/3/7 12:34, Joonsoo Kim wrote:
> > On Fri, Mar 04, 2016 at 03:35:26PM +0800, Hanjun Guo wrote:
> > > On 2016/3/4 14:38, Joonsoo Kim wrote:
> > > > On Fri, Mar 04, 2016 at 02:05:09PM +0800, Hanjun Guo wrote:
> > > > > On 2016/3/4 12:32, Joonsoo Kim wrote:
> > > > > > On Fri, Mar 04, 2016 at 11:02:33AM +0900, Joonsoo Kim wrote:
> > > > > > > On Thu, Mar 03, 2016 at 08:49:01PM +0800, Hanjun Guo wrote:
> > > > > > > > On 2016/3/3 15:42, Joonsoo Kim wrote:
> > > > > > > > > 2016-03-03 10:25 GMT+09:00 Laura Abbott <labbott@xxxxxxxxxx>:
> > > > > > > > > > (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:
> > > > > > > Thanks! Now, I can re-generate erronous situation you mentioned.
> > > > > > >
> > > > > > > >   - 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:
> > > > > > > [1] would not be sufficient to close this race.
> > > > > > >
> > > > > > > Try following things [A]. And, for more accurate test, I changed code a bit more
> > > > > > > to prevent kernel page allocation from cma area [B]. This will prevent kernel
> > > > > > > page allocation from cma area completely so we can focus cma_alloc/release race.
> > > > > > >
> > > > > > > Although, this is not correct fix, it could help that we can guess
> > > > > > > where the problem is.
> > > > > > More correct fix is something like below.
> > > > > > Please test it.
> > > > > Hmm, this is not working:
> > > > Sad to hear that.
> > > >
> > > > Could you tell me your system's MAX_ORDER and pageblock_order?
> > >
> > > MAX_ORDER is 11, pageblock_order is 9, thanks for your help!
> >
> > Hmm... that's same with me.
> >
> > Below is similar fix that prevents buddy merging when one of buddy's
> > migrate type, but, not both, is MIGRATE_ISOLATE. In fact, I have
> > no idea why previous fix (more correct fix) doesn't work for you.
> > (It works for me.) But, maybe there is a bug on the fix
> > so I make new one which is more general form. Please test it.
>
> Hi,
> 	Hanjun Guo has gone to Tailand on business, so I help him to run this patch. The result
> shows that the count of "CmaFree:" is OK now.

Thanks Leizhen :)

> But sometimes printed some information as below:
>
> alloc_contig_range: [28500, 28600) PFNs busy
> alloc_contig_range: [28300, 28380) PFNs busy

I think it's not a problem for the stress test, as it's
the lock not released yet.

Thanks
Hanjun