linux-kernel - Re: [patch 1/4] mempolicy: convert MPOL constants to enum

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Message-ID: <Pine.LNX.4.64.0802111146590.25590@schroedinger.engr.sgi.com>
Date:	Mon, 11 Feb 2008 11:48:59 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	David Rientjes <rientjes@...gle.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Jackson <pj@....com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] mempolicy: convert MPOL constants to enum

On Mon, 11 Feb 2008, David Rientjes wrote:

> > The second paragraphs seems to indicate that such an approach does not 
> > work since we also use MPOL_xx constants to set flags in the memory 
> > policies?
> > 
> 
> Not sure I'm understanding your question, sorry.
> 
> Mempolicy modes have always been int constants because it doesn't make 
> sense to combine them.  Putting them into 'enum mempolicy_mode' leaves 
> that unchanged.

> Mempolicy flags can be combined (even though my patchset only currently 
> implements one, it's easy to implement others).  So they definitely cannot 
> be enum constants.

> Regardless, storing the policy (mode | flags) in struct mempolicy as a 
> 'short' doesn't help since a negative policy doesn't mean anything.  In 
> preparation for allowing the upper MPOL_FLAG_SHIFT bits to be used to 
> store the flags of this member, I converted it to 'unsigned short'.  This 
> is because the API with userspace is through 'int', which is implicitly 
> signed, and we don't want to sign-extend the upper bit if it's ever used 
> to hold a mempolicy flag.

Then you could follow through with the enum mempolicy thing 
throughtout. Why not use enum mempolicy in struct mempolicy?


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