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

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Message-Id: <20080328105406.5dc61c6c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 28 Mar 2008 10:54:06 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Yasunori Goto <y-goto@...fujitsu.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>, 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 Fri, 28 Mar 2008 10:34:51 +0900
Yasunori Goto <y-goto@...fujitsu.com> wrote:
> > > 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.
> 
Ah, ok. sorry.

Jeremy, I think you can check whether you have 'struct page' or not by
pfn_valid(). 

If pfn_valid() == false, you should call add_memory() and create
a section/mem_map. If pfn_valid() == true, you should just remove
PG_reserved bit in mem_map by online_page().

Thanks,
-Kame

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