linux-kernel - Re: [patch 20/20] Add apply_to_page_range() which applies a function to a pte range.

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Message-ID: <20070417205652.GM11115@waste.org>
Date:	Tue, 17 Apr 2007 15:56:52 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andi Kleen <ak@...e.de>, Andrew Morton <akpm@...ux-foundation.org>,
	virtualization@...ts.osdl.org, lkml <linux-kernel@...r.kernel.org>,
	Ian Pratt <ian.pratt@...source.com>,
	Christian Limpach <Christian.Limpach@...cam.ac.uk>,
	Chris Wright <chrisw@...s-sol.org>,
	Christoph Lameter <clameter@....com>,
	Matt Mackall <mpm@...te.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 20/20] Add apply_to_page_range() which applies a function to a pte range.

On Wed, Apr 04, 2007 at 11:52:57PM -0700, Jeremy Fitzhardinge wrote:
> Matt Mackall wrote:
> >> +/*
> >> + * Scan a region of virtual memory, filling in page tables as necessary
> >> + * and calling a provided function on each leaf page table.
> >> + */
> >>     
> >
> > But I'm not sure what the use case is that wants filling in the page
> > table..? If both modes really make sense, perhaps a flag could unify
> > these differences.
> >   
> 
> Well, two reasons:
> 
> One is the general one that if you're traversing ptes then they need to
> exist to traverse them (for example, if you're creating new mappings). 
> Obviously if you want to just visit existing mappings, then
> instantiating new pagetable is not the right thing to do (and I could
> make use of this too).
> 
> The other is that there are various places in the Xen hypervisor API
> where you pass in a reference to pte entry for the hypervisor to put
> mappings into, and the rest of the pagetable needs to exist.  The Xen
> code uses the side-effect of apply_to_page_range() to create pagetable
> for these calls.

I think adding a flags field and an allocate flag to my callback
struct would be sufficient here.

> > I'd gotten the impression that these sorts of typedefs were out of
> > fashion.
> >   
> 
> In general yes, but for function pointers the syntax is so clumsy that I
> think typedefs are OK.

The syntax is horrible, but I don't think we end up using the
resultant type enough to justify the namespace pollution.

-- 
Mathematics is the supreme nostalgia of our time.
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