Re: freepage accounting bug with CMA/migrate isolation

[Mike Kravetz <mike.kravetz@oracle.com>]

On 07/24/2018 03:38 PM, Laura Abbott wrote:
> On 07/23/2018 09:24 PM, Mike Kravetz wrote:
>> With v4.17, I can see an issue like those addressed in commits 3c605096d315
>> ("mm/page_alloc: restrict max order of merging on isolated pageblock")
>> and d9dddbf55667 ("mm/page_alloc: prevent merging between isolated and
>> other pageblocks").  After running a CMA stress test for a while, I see:
>>    MemTotal:        8168384 kB
>>    MemFree:         8457232 kB
>>    MemAvailable:    9204844 kB
>> If I let the test run, MemFree and MemAvailable will continue to grow.
>>
>> I am certain the issue is with pageblocks of migratetype ISOLATED.  If
>> I disable all special 'is_migrate_isolate' checks in freepage accounting,
>> the issue goes away.  Further, I am pretty sure the issue has to do with
>> pageblock merging and or page orders spanning pageblocks.  If I make
>> pageblock_order equal MAX_ORDER-1, the issue also goes away.
>>
>> Just looking for suggesting in where/how to debug.  I've been hacking on
>> this without much success.
>> -- 
>> Mike Kravetz
>>
> 
> If you revert d883c6cf3b39 ("Revert "mm/cma: manage the memory of the CMA
> area by using the ZONE_MOVABLE"") do you still see the issue? I thought
> there was another isolation edge case which was fixed by that series.
> 

Thanks Laura,

Reverting that patch certainly seems to help.  Although, I'm guessing there
is still some accounting issue even with the patch reverted.

Right after boot,
MemTotal:        8168380 kB
MemFree:         7233360 kB
MemAvailable:    7317704 kB

After stress testing for a couple hours,
MemTotal:        8168380 kB
MemFree:         7848468 kB
MemAvailable:    7634856 kB

While looking at the code, I did not like the way set_migratetype_isolate
may 'isolate' more than pageblock_nr_pages if there is a > pageblock_order
sized free page.  This seems to work because alloc_contig_range always
aligns to MAX_ORDER-1.  But, I'd like to change this and see if it helps.

-- 
Mike Kravetz