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

[Jeremy Fitzhardinge]

KAMEZAWA Hiroyuki wrote:
> On Fri, 28 Mar 2008 10:34:51 +0900
> Yasunori Goto <y-goto@xxxxxxxxxxxxxx> 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().

OK.  Would that ever be necessary if I explicitly align my start and size?

   J

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