linux-kernel - Re: [PATCH] x86: create array based interface to change page attribute

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Message-Id: <1207100134.7250.21.camel@clockmaker.usersys.redhat.com>
Date:	Wed, 02 Apr 2008 11:35:34 +1000
From:	Dave Airlie <airlied@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Dave Airlie <airlied@...il.com>, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, arjan@...ux.intel.com,
	thomas@...gstengraphics.com
Subject: Re: [PATCH] x86: create array based interface to change page
	attribute


On Mon, 2008-03-31 at 13:46 +0200, Andi Kleen wrote:
> On Mon, Mar 31, 2008 at 09:21:19PM +1000, Dave Airlie wrote:
> > On Mon, Mar 31, 2008 at 5:25 PM, Andi Kleen <andi@...stfloor.org> wrote:
> > > Dave Airlie <airlied@...hat.com> writes:
> > >  >
> > >  > +#define CPA_FLUSHTLB 1
> > >  > +#define CPA_ARRAY 2
> > >
> > >  I don't think CPA_ARRAY should be a separate case. Rather single
> > >  page flushing should be an array with only a single entry. pageattr
> > >  is already very complex, no need to make add more special cases.
> > 
> > I thought about this but the current interface takes a start address
> > and number of pages from that point to cpa,
> > the array interface takes an array of page sized pages.
> > 
> > I don't really think we need to generate an array in the first case
> > with all the pages in it..
> 
> Just put the length into the array members too.

I can only think to do this by maybe stealing some bits, and having the
caller provide a pfn + length in one 64-bit dword.

As otherwise I'm going to end up with the largest use case for this
having to allocate a large array of 64-bit dwords all containing 1.

This isn't worth it IMHO and the array doesn't add that much more
complexity.

Dave.

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