linux-kernel - Re: [PATCH 21/41] CacheFiles: Permit the page lock state to be monitored [ver #48]

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Date:	Sat, 04 Apr 2009 23:13:33 +0100
From:	David Howells <dhowells@...hat.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	dhowells@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, nfsv4@...ux-nfs.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 21/41] CacheFiles: Permit the page lock state to be monitored [ver #48]

Nick Piggin <nickpiggin@...oo.com.au> wrote:

> 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...

What is not such a bad concept to have?  Having an extra page flag?

> actually we already have exactly this concept which is what should be used.
> Ie. the filesystem's io completion handler.

Which filesystem's I/O completion handler?

David
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