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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 23/43] CacheFiles: Permit the page lock state to be monitored [ver #46]
Date: Fri, 3 Apr 2009 02:37:25 +1100
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Cc: viro@zeniv.linux.org.uk, nfsv4@linux-nfs.org, linux-kernel@vger.kernel.org,
       linux-fsdevel@vger.kernel.org
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On Thursday 02 April 2009 10:05:20 David Howells wrote:
> Add a function to install a monitor on the page lock waitqueue for a particular
> page, thus allowing the page being unlocked to be detected.
> 
> This is used by CacheFiles to detect read completion on a page in the backing
> filesystem so that it can then copy the data to the waiting netfs page.

I prefer to nack this because it is exporting details of the page
locking mechanism. unlock_page is very heavyweight in large part
because of the memory barriers and cacheline required to check the
waitqueue. I have patches to avoid all that if the page lock is
not contended.

What's wrong with using wait_on_page_locked, like everyone else does?
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