Re: dirty balancing deadlock
From: Miklos Szeredi
Date: Mon Feb 19 2007 - 12:12:47 EST
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()
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.
--- 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
+ * 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)
dirty_exceeded = 1;
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