linux-kernel - RE: [RFC] transcendent memory for Linux

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Date:	Mon, 29 Jun 2009 14:13:56 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Pavel Machek <pavel@....cz>
Cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	npiggin@...e.de, chris.mason@...cle.com, kurt.hackel@...cle.com,
	dave.mccracken@...cle.com, Avi Kivity <avi@...hat.com>,
	jeremy@...p.org, Rik van Riel <riel@...hat.com>,
	alan@...rguk.ukuu.org.uk, Rusty Russell <rusty@...tcorp.com.au>,
	Martin Schwidefsky <schwidefsky@...ibm.com>, akpm@...l.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	tmem-devel@....oracle.com, sunil.mushran@...cle.com,
	linux-mm@...ck.org, Himanshu Raj <rhim@...rosoft.com>
Subject: RE: [RFC] transcendent memory for Linux

> > It is documented currently at:
> > 
> > http://oss.oracle.com/projects/tmem/documentation/api/
> > 
> > (just noticed I still haven't posted version 0.0.2 which
> > has a few minor changes).
> > 
> > I will add a briefer description of this API in Documentation/
> 
> Please do.

OK, will do.

> At least TMEM_NEW_POOL() looks quite ugly. Why uuid? Mixing flags into
> size argument is strange.

The uuid is only used for shared pools.  If two different
"tmem clients" (guests) agree on a 128-bit "shared secret",
they can share a tmem pool.  For ocfs2, the 128-bit uuid in
the on-disk superblock is used for this purpose to implement
shared precache.  (Pages evicted by one cluster node
can be used by another cluster node that co-resides on
the same physical system.)

The (page)size argument is always fixed (at PAGE_SIZE) for
any given kernel.  The underlying implementation can
be capable of supporting multiple pagesizes.

So for the basic precache and preswap uses, "new pool"
has a very simple interface.

> > It is in-kernel only because some of the operations have
> > a parameter that is a physical page frame number.
> 
> In-kernel API is probably better described as function prototypes.

Good idea.  I will do that.

Thanks,
Dan
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