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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 21/41] CacheFiles: Permit the page lock state to be monitored [ver #48]
Date: Sun, 5 Apr 2009 01:22:41 +1100
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Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       nfsv4@linux-nfs.org, linux-fsdevel@vger.kernel.org
References: <20090403155436.28714.23368.stgit@warthog.procyon.org.uk> <20090403155624.28714.87176.stgit@warthog.procyon.org.uk> <200904041709.31651.nickpiggin@yahoo.com.au>
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On Saturday 04 April 2009 17:09:31 Nick Piggin wrote:
> On Saturday 04 April 2009 02:56:24 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.
> 
> This is the only thing I'm still worried about in core code. The extra
> page flag (which is probably unusable for any other fs, due to its
> semantics) is an issue, but Andrew seemed like he was willing to spend
> *2* page flags on this, so I'm sure he's happy with 1.

Well that is to say it is not a such a bad concept to have... actually
we already have exactly this concept which is what should be used. Ie.
the filesystem's io completion handler.
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