linux-kernel - Re: PS3: trouble with SPARSEMEM

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Date:	Fri, 07 Dec 2007 18:47:04 -0800
From:	Geoff Levand <geoffrey.levand@...sony.com>
To:	Yasunori Goto <y-goto@...fujitsu.com>
CC:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>,
	Andrew Morton <akpm@...ux-foundation.org>, miltonm@....com,
	clameter@....com, apw@...dowen.org, linux-kernel@...r.kernel.org
Subject: Re: PS3: trouble with SPARSEMEM_VMEMMAP and kexec

Yasunori Goto wrote:
>> On Thu, 6 Dec 2007, Geert Uytterhoeven wrote:
>> > On Thu, 6 Dec 2007, Yasunori Goto wrote:
>> > > > I'll try Milton's suggestion to pre-allocate the memory early.  It seems
>> > > > that should work as long as nothing else before the hot-plug mem is added
>> > > > needs a large chunk.
>> > > 
>> > > Hello. Geoff-san. Sorry for late response.
>> > > 
>> > > Could you tell me the value of the following page_size calculation
>> > > in vmemmap_populate()? I think this page_size may be too big value. 
>> > > 
>> > > ------
>> > > int __meminit vmemmap_populate(struct page *start_page,
>> > >                                        unsigned long nr_pages, int node)
>> > >                            :
>> > >                            :
>> > >         unsigned long page_size = 1 << mmu_psize_defs[mmu_linear_psize].shift;
>> > >                            :
>> > > -------
>> 
>> 16 MiB of course.
> 
> 16 MiB is not page size. It is "section size". 
> IIRC, powerpc's page size must be 4K (or 64K).
> If page size is 4k, vmemmap_alloc_block will call the order 12 page.


By default PS3 uses 4K virtual pages, and 16M linear pages.


> Is it really correct value for vmemmap population?


It seems vmemmap needs linear pages, so I think it is ok.


>> PS3 initially starts with 128 MiB.
>> Later hotplug is used to add the remaining memory (96 or 112 MIB, IIRC).
> 
> Ok.
> Then, add_memory() must be called 6 or 7 times for each sections.


Yes, I call add_memory() once, then it in turn calls sparse_add_one_section()
7 times.

-Geoff


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