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Re: [PATCH 02/27] xfs: remove the unused ilock_nowait codepath in writep

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 02/27] xfs: remove the unused ilock_nowait codepath in writepage
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Thu, 30 Jun 2011 02:55:29 -0400
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20110630001525.GU561@dastard>
References: <20110629140109.003209430@xxxxxxxxxxxxxxxxxxxxxx> <20110629140336.717434334@xxxxxxxxxxxxxxxxxxxxxx> <20110630001525.GU561@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Jun 30, 2011 at 10:15:25AM +1000, Dave Chinner wrote:
> On Wed, Jun 29, 2011 at 10:01:11AM -0400, Christoph Hellwig wrote:
> > wbc->nonblocking is never set, so this whole code has been unreachable
> > for a long time.  I'm also not sure it would make a lot of sense -
> > we'd rather finish our writeout after a short wait for the ilock
> > instead of cancelling the whole ioend.
> 
> I'd suggest that the only thing that should be dropped is the
> wbc->nonblocking check. Numbers would be good to validate that this
> is still relevant, but I don't have a storage subsystem with enough
> bandwidth to drive a flusher thread to being CPU bound...

I don't mind re-introducing this if we actuall have a testcase for it.
Note that simply keeping the code won't work for the writepages
implementation as we'd cancel the whole ioend if one lock fails,
discarding potentially a lot of I/O.  It's already bad enough with
the simpler clustering we have in the current code.  Back in SLES10 /
2.6.16 when the code could still be reached we only did it for the
bmap calls directly from writepage, but not from the writeout
clustering.

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