Re: freepage accounting bug with CMA/migrate isolation

[Vlastimil Babka <vbabka@suse.cz>]

On 07/24/2018 06:24 AM, 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.

That means you count isolated pages as freepages, right?

> 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.

Interesting, that should only matter in __free_one_page(). Do you have
page guards enabled?

> Just looking for suggesting in where/how to debug.  I've been hacking on
> this without much success.
> --
> Mike Kravetz
>