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From: Miklos Szeredi <miklos@szeredi.hu>
To: akpm@linux-foundation.org
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: dirty balancing deadlock
Date: Mon, 19 Feb 2007 18:11:55 +0100	[thread overview]
Message-ID: <E1HJC3P-0006tz-00@dorka.pomaz.szeredi.hu> (raw)
In-Reply-To: <20070218155916.0d3c73a9.akpm@linux-foundation.org> (message from Andrew Morton on Sun, 18 Feb 2007 15:59:16 -0800)

How about this?

Solves the FUSE deadlock, but not the throttle_vm_writeout() one.
I'll try to tackle that one as well.

If the per-bdi dirty counter goes below 16, balance_dirty_pages()
returns.

Does the constant need to tunable?  If it's too large, then the global
threshold is more easily exceeded.  If it's too small, then in a tight
situation progress will be slower.

Thanks,
Miklos

Index: linux/mm/page-writeback.c
===================================================================
--- linux.orig/mm/page-writeback.c	2007-02-19 17:32:41.000000000 +0100
+++ linux/mm/page-writeback.c	2007-02-19 18:05:28.000000000 +0100
@@ -198,6 +198,25 @@ static void balance_dirty_pages(struct a
 			dirty_thresh)
 				break;
 
+		/*
+		 * Acquit this producer if there's little or nothing
+		 * to write back to this particular queue
+		 *
+		 * Without this check a deadlock is possible in the
+		 * following case:
+		 *
+		 * - filesystem A writes data through filesystem B
+		 * - filesystem A has dirty pages over dirty_thresh
+		 * - writeback is started, this triggers a write in B
+		 * - balance_dirty_pages() is called synchronously
+		 * - the write to B blocks
+		 * - the writeback completes, but dirty is still over threshold
+		 * - the blocking write prevents futher writes from happening
+		 */
+		if (atomic_long_read(&bdi->nr_dirty) +
+		    atomic_long_read(&bdi->nr_writeback) < 16)
+			break;
+
 		if (!dirty_exceeded)
 			dirty_exceeded = 1;
 

  parent reply	other threads:[~2007-02-19 17:12 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-18 18:28 Miklos Szeredi
2007-02-18 20:53 ` Andrew Morton
2007-02-18 21:25   ` Rik van Riel
2007-02-18 22:54     ` Miklos Szeredi
2007-02-18 22:50   ` Miklos Szeredi
2007-02-18 22:59     ` Andrew Morton
2007-02-18 23:22       ` Miklos Szeredi
2007-02-18 23:59         ` Andrew Morton
2007-02-19  0:25           ` Miklos Szeredi
2007-02-19  0:30             ` Miklos Szeredi
2007-02-19  0:45             ` Miklos Szeredi
2007-02-19  0:45             ` Chris Mason
2007-02-19  0:54               ` Miklos Szeredi
2007-02-19  1:01                 ` Chris Mason
2007-02-19  1:14                   ` Miklos Szeredi
2007-02-20  0:16                     ` Chris Mason
2007-02-20  8:53                       ` Miklos Szeredi
2007-02-19 17:11           ` Miklos Szeredi [this message]
2007-02-19 23:12             ` Miklos Szeredi
2007-02-20  0:13             ` Chris Mason
2007-02-20  8:47               ` Miklos Szeredi
2007-02-20 11:30                 ` Chris Mason
2007-02-21 21:36             ` Andrew Morton
2007-02-22  7:42               ` Miklos Szeredi
2007-02-22  7:55                 ` Andrew Morton
2007-02-22  8:02                   ` Miklos Szeredi

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