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Date:	Thu, 28 Apr 2011 14:42:20 +0100
From:	Colin Ian King <colin.king@...ntu.com>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	James Bottomley <james.bottomley@...e.de>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [BUG] fatal hang untarring 90GB file, possibly writeback
 related.


On Thu, 2011-04-28 at 08:29 -0400, Chris Mason wrote:
> Excerpts from Colin Ian King's message of 2011-04-28 07:36:30 -0400:
> > One more data point to add, I've been looking at an identical issue when
> > copying large amounts of data.  I bisected this - and the lockups occur
> > with commit 
> > 3e7d344970673c5334cf7b5bb27c8c0942b06126 - before that I don't see the
> > issue. With this commit, my file copy test locks up after ~8-10
> > iterations, before this commit I can copy > 100 times and don't see the
> > lockup.
> 
> Well, that's really interesting.  I tried with compaction on here and
> couldn't trigger it, but this (very very lightly) tested patch might
> help.
> 
Thanks Chris,

I've given this a soak test but I still see the same lockup.

> It moves the writeout throttle before the goto restart, and also makes
> sure we do at least one cond_resched before we loop.
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 6771ea7..cb08b41 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1934,12 +1934,14 @@ restart:
>  	if (inactive_anon_is_low(zone, sc))
>  		shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
>  
> +	throttle_vm_writeout(sc->gfp_mask);
> +
>  	/* reclaim/compaction might need reclaim to continue */
>  	if (should_continue_reclaim(zone, nr_reclaimed,
> -					sc->nr_scanned - nr_scanned, sc))
> +					sc->nr_scanned - nr_scanned, sc)) {
> +		cond_resched();
>  		goto restart;
> -
> -	throttle_vm_writeout(sc->gfp_mask);
> +	}
>  }
>  
>  /*


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