linux-kernel - Re: [PATCH 2 of 4] hotplug-memory: adding non-section-aligned memory is bad

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Message-Id: <20080328102342.B0BF.E1E9C6FF@jp.fujitsu.com>
Date:	Fri, 28 Mar 2008 10:34:51 +0900
From:	Yasunori Goto <y-goto@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Christoph Lameter <clameter@....com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2 of 4] hotplug-memory: adding non-section-aligned memory is bad

> On Thu, 27 Mar 2008 17:28:38 -0700
> Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -784,6 +784,9 @@
> >  #define PAGES_PER_SECTION       (1UL << PFN_SECTION_SHIFT)
> >  #define PAGE_SECTION_MASK	(~(PAGES_PER_SECTION-1))
> >  
> > +#define SECTION_SIZE		(1UL << SECTION_SIZE_BITS)
> > +#define SECTION_SIZE_MASK	(SECTION_SIZE - 1)
> > +
> >  #define SECTION_BLOCKFLAGS_BITS \
> >  	((1UL << (PFN_SECTION_SHIFT - pageblock_order)) * NR_PAGEBLOCK_BITS)
> >  
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -300,6 +300,11 @@
> >  	int ret;
> >  	u64 start = res->start;
> >  	u64 size = res->end - res->start + 1;
> > +
> > +	/* Adding non-section-aligned memory will give unexpected
> > +	   and unintuitive results. */
> > +	WARN_ON((start & SECTION_SIZE_MASK) != 0);
> > +	WARN_ON((size & SECTION_SIZE_MASK) != 0);
> >  
> Why just WARNING ? not BUG_ON?

Both Nack.

Because, firmware may occupy some area in the section.
Firmware must exclude those area to notify kernel. So, E820, EFI,
or _CRS of ACPI may return not aligned address and size.
register_memory_resource() and walk_memory_resource() are to skip
them silently. This is intended.

Bye.

-- 
Yasunori Goto 


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