linux-kernel - Re: [PATCH 23/43] CacheFiles: Permit the page lock state to be monitored [ver #46]

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Message-Id: <200904030237.25893.nickpiggin@yahoo.com.au>
Date:	Fri, 3 Apr 2009 02:37:25 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	David Howells <dhowells@...hat.com>
Cc:	viro@...iv.linux.org.uk, nfsv4@...ux-nfs.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 23/43] CacheFiles: Permit the page lock state to be monitored [ver #46]

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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