Re: [patch for-4.7] mm, compaction: prevent VM_BUG_ON when terminating freeing scanner

[Minchan Kim]

On Wed, Jun 29, 2016 at 02:47:20PM -0700, David Rientjes wrote:
> It's possible to isolate some freepages in a pageblock and then fail 
> split_free_page() due to the low watermark check.  In this case, we hit 
> VM_BUG_ON() because the freeing scanner terminated early without a 
> contended lock or enough freepages.
> 
> This should never have been a VM_BUG_ON() since it's not a fatal 
> condition.  It should have been a VM_WARN_ON() at best, or even handled 
> gracefully.
> 
> Regardless, we need to terminate anytime the full pageblock scan was not 
> done.  The logic belongs in isolate_freepages_block(), so handle its state
> gracefully by terminating the pageblock loop and making a note to restart 
> at the same pageblock next time since it was not possible to complete the 
> scan this time.
> 
> Reported-by: Minchan Kim <minchan@xxxxxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Tested-by: Minchan Kim <minchan@xxxxxxxxxx>

I don't know you sill send updated version based on Joonsoo again.
Anyway, this patch itself doesn't trigger VM_BUG_ON in my test. 

Thanks.