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Date: Wed, 2 Jun 2010 08:35:43 -0700 (PDT)
From: Dan Magenheimer <dan.magenheimer@oracle.com>
To: Jamie Lokier <jamie@shareable.org>
Cc: chris.mason@oracle.com, viro@zeniv.linux.org.uk, akpm@linux-foundation.org,
       adilger@sun.com, tytso@mit.edu, mfasheh@suse.com,
       joel.becker@oracle.com, matthew@wil.cx, linux-btrfs@vger.kernel.org,
       linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
       linux-ext4@vger.kernel.org, ocfs2-devel@oss.oracle.com,
       linux-mm@kvack.org, ngupta@vflare.org, jeremy@goop.org,
       JBeulich@novell.com, kurt.hackel@oracle.com, npiggin@suse.de,
       dave.mccracken@oracle.com, riel@redhat.com, avi@redhat.com,
       konrad.wilk@oracle.com
Subject: RE: [PATCH V2 0/7] Cleancache (was Transcendent Memory): overview
References: <20100528173510.GA12166@ca-server1.us.oracle.com
 20100602130014.GB7238@shareable.org>
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> From: Jamie Lokier [mailto:jamie@shareable.org]
> Subject: Re: [PATCH V2 0/7] Cleancache (was Transcendent Memory):
> overview
> 
> Dan Magenheimer wrote:
> > Most important, cleancache is "ephemeral".  Pages which are copied
> into
> > cleancache have an indefinite lifetime which is completely unknowable
> > by the kernel and so may or may not still be in cleancache at any
> later time.
> > Thus, as its name implies, cleancache is not suitable for dirty
> pages.  The
> > pseudo-RAM has complete discretion over what pages to preserve and
> what
> > pages to discard and when.
> 
> Fwiw, the feature sounds useful to userspace too, for those things
> with memory hungry caches like web browsers.  Any plans to make it
> available to userspace?

No plans yet, though we agree it sounds useful, at least for
apps that bypass the page cache (e.g. O_DIRECT).  If you have
time and interest to investigate this further, I'd be happy
to help.  Send email offlist.

Thanks,
Dan
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