linux-kernel - Re: [patch 2/2] convert s390 page handling macros to functions v3

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Message-ID: <20060911042201.GA8379@osiris.ibm.com>
Date:	Mon, 11 Sep 2006 06:22:01 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Dave Hansen <haveblue@...ibm.com>
Cc:	Roman Zippel <zippel@...ux-m68k.org>,
	Andrew Morton <akpm@...l.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [patch 2/2] convert s390 page handling macros to functions v3

On Sun, Sep 10, 2006 at 09:25:18AM -0700, Dave Hansen wrote:
> On Sun, 2006-09-10 at 15:08 +0200, Heiko Carstens wrote:
> > 
> > +static inline int page_test_and_clear_dirty(struct page *page)
> > +{
> > +       unsigned long physpage = __pa((page - mem_map) << PAGE_SHIFT);
> > +       int skey = page_get_storage_key(physpage); 
> 
> This has nothing to do with your patch at all, but why is 'page -
> mem_map' being open-coded here?

I just changed the defines to functions without thinking about this.. :)

> I see at least a couple of page_to_phys() definitions on some
> architectures.  This operation is done enough times that s390 could
> probably use the same treatment.

Yes, even s390 has page_to_phys() as well. But why is it in io.h? Seems
like this is inconsistent across architectures. Also in quite a few
architectures the define looks like this:

#define page_to_phys(page)	((page - mem_map) << PAGE_SHIFT)

A pair of braces is missing around page. Yet another possible subtle bug...

> It could at least use a page_to_pfn() instead of the 'page - mem_map'
> operation, right?

Yes, I will address that in a later patch. Shouldn't stop this one from
being merged, if there aren't any other objections.
Thanks for pointing this out!
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