linux-kernel - Re: [PATCH -mm -v4 1/3] i386/x86

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Message-Id: <1191918139.9719.47.camel@caritas-dev.intel.com>
Date:	Tue, 09 Oct 2007 16:22:19 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	linux-mm@...ck.org, "H. Peter Anvin" <hpa@...or.com>,
	Andi Kleen <ak@...e.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	akpm@...ux-foundation.org, Yinghai Lu <yhlu.kernel@...il.com>,
	Chandramouli Narayanan <mouli@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm -v4 1/3] i386/x86_64 boot: setup data

On Tue, 2007-10-09 at 01:25 +1000, Nick Piggin wrote:
> On Tuesday 09 October 2007 16:40, Huang, Ying wrote:
> 
> > +unsigned long copy_from_phys(void *to, unsigned long from_phys,
> > +			     unsigned long n)
> > +{
> > +	struct page *page;
> > +	void *from;
> > +	unsigned long remain = n, offset, trunck;
> > +
> > +	while (remain) {
> > +		page = pfn_to_page(from_phys >> PAGE_SHIFT);
> > +		from = kmap_atomic(page, KM_USER0);
> > +		offset = from_phys & ~PAGE_MASK;
> > +		if (remain > PAGE_SIZE - offset)
> > +			trunck = PAGE_SIZE - offset;
> > +		else
> > +			trunck = remain;
> > +		memcpy(to, from + offset, trunck);
> > +		kunmap_atomic(from, KM_USER0);
> > +		to += trunck;
> > +		from_phys += trunck;
> > +		remain -= trunck;
> > +	}
> > +	return n;
> > +}
> 
> 
> I suppose that's not unreasonable to put in mm/memory.c, although
> it's not really considered a problem to do this kind of stuff in
> a low level arch file...
> 
> You have no kernel virtual mapping for the source data?
> 

On 32-bit platform such as i386. Some memory zones have no kernel
virtual mapping (highmem region etc). So I think this may be useful as a
universal way to access physical memory. But it can be more efficient to
implement it in arch file for some arch. Should this implementation be
used as a fall back implementation with attribute "weak"?

> Should it be __init?
> 
> Care to add a line of documentation if you keep it in mm/memory.c?
> 

OK, I will add the document in the next version.

Best Regards,
Huang Ying
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