linux-ext4 - Re: [PATCH V2 2/7] Cleancache (was Transcendent Memory): core files

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Message-ID: <4C06F571.3050306@goop.org>
Date:	Wed, 02 Jun 2010 17:21:05 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, chris.mason@...cle.com,
	viro@...iv.linux.org.uk, adilger@....COM, tytso@....edu,
	mfasheh@...e.com, joel.becker@...cle.com, matthew@....cx,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	ocfs2-devel@....oracle.com, linux-mm@...ck.org, ngupta@...are.org,
	JBeulich@...ell.com, kurt.hackel@...cle.com, npiggin@...e.de,
	dave.mccracken@...cle.com, riel@...hat.com, avi@...hat.com,
	konrad.wilk@...cle.com
Subject: Re: [PATCH V2 2/7] Cleancache (was Transcendent Memory): core files

On 06/02/2010 05:06 PM, Dan Magenheimer wrote:
> It is intended that there be different flavours but only
> one can be used in any running kernel.  A driver file/module
> claims the cleancache_ops pointer (and should check to ensure
> it is not already claimed).  And if nobody claims cleancache_ops,
> the hooks should be as non-intrusive as possible.
>
> Also note that the operations occur on the order of the number
> of I/O's, so definitely a lot, but "zillion" may be a bit high. :-)
>
> If you think this is a showstoppper, it could be changed
> to be bound only at compile-time, but then (I think) the claimer
> could never be a dynamically-loadable module.
>   

Andrew is suggesting that rather than making cleancache_ops a pointer to
a structure, just make it a structure, so that calling a function is a
matter of cleancache_ops.func rather than cleancache_ops->func, thereby
avoiding a pointer dereference.

    J
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