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Date: Wed, 13 Jul 2011 03:57:40 -0700 (PDT)
From: Hugh Dickins <hughd@google.com>
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To: Wu Fengguang <fengguang.wu@intel.com>
cc: Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
        Mel Gorman <mel@csn.ul.ie>, Dave Chinner <david@fromorbit.com>,
        Christoph Hellwig <hch@infradead.org>,
        Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 12/15] writeback: remove writeback_control.more_io
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On Tue, 12 Jul 2011, Hugh Dickins wrote:
> On Tue, 12 Jul 2011, Hugh Dickins wrote:
> > On Mon, 11 Jul 2011, Wu Fengguang wrote:
> > > 
> > > It's relatively easy to confirm, by reusing the below trace event to
> > > show the inode (together with its state) being requeued.
> > > 
> > > If this is the root cause, it may equally be fixed by
> > > 
> > > -			requeue_io(inode, wb);
> > > +			redirty_tail(inode, wb);
> > > 
> > > which would be useful in case the bug is so deadly that it's no longer
> > > possible to do tracing.
> > 
> > I checked again this morning that I could reproduce it on two machines,
> > one went in a few minutes, the other within the hour.  Then I made that
> > patch changing the requeue_io to redirty_tail, and left home with them
> > running the test with the new kernel: we'll see at the end of the day
> > how they fared.
> 
> I think that fixes it.  The x86_64 is still running with that, but the
> ppc64 gave up fairly early, hitting freeze in __slab_free() instead.
> 
> I've now, I believe, reconstituted what ChristophL intended from the
> mm_types.h struct page patch he posted (which applied neither to mmotm,
> nor to Pekka's for-next, so far as I could tell: maybe cl did some
> intermediate tidying of some of the random indentation).  So now
> testing that with redirty_tail on ppc64: will report in 9 hours.

Same result as before.  The x86_64 is still going fine, but the ppc64
again seized up in __slab_free() after two and a half hours of load.

I think we should assume that your -requeue_io +redirty_tail is a good
fix for the writeback freeze (if you can reassure us, that it does not
risk postponing some writes indefinitely), and I move over to the other
thread to pursue the struct page __slab_free() freeze.

Thanks!
Hugh