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Date:	Thu, 28 Apr 2011 08:29:29 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	Colin Ian King <colin.king.lkml@...il.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.

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.

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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