linux-kernel - Re: [patch for-4.7] mm, compaction: prevent VM_BUG

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Message-ID: <20160706065016.GA16614@bbox>
Date:	Wed, 6 Jul 2016 15:50:16 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
CC:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<hughd@...gle.com>, <mgorman@...hsingularity.net>,
	<stable@...r.kernel.org>, <vbabka@...e.cz>
Subject: Re: [patch for-4.7] mm, compaction: prevent VM_BUG_ON when
 terminating freeing scanner

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@...nel.org>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
Tested-by: Minchan Kim <minchan@...nel.org>

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.