linux-kernel - Re: PS3: trouble with SPARSEMEM

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Message-Id: <20071206142552.694B.Y-GOTO@jp.fujitsu.com>
Date:	Thu, 06 Dec 2007 15:09:38 +0900
From:	Yasunori Goto <y-goto@...fujitsu.com>
To:	Geoff Levand <geoffrey.levand@...sony.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>,
	miltonm@....com, clameter@....com, apw@...dowen.org,
	linux-kernel@...r.kernel.org
Subject: Re: PS3: trouble with SPARSEMEM_VMEMMAP and kexec

> 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;
                           :
-------

In addition, I remember that current add_memory() is designed for
only 1 section's addition. (See: memory_probe_store() and
sparse_mem_map_populate().
they require only for 1 section's mem_map by specifing
PAGES_PER_SECTION.)
The 1 section size for normal powerpc box is only 16MB.
(IA64 -> 1GB, x86-64 -> 128MB).

But, if my understanding is correct, PS3's add_memory() requires all
of total memory. I'm afraid something other problems might be hidden
in this issue yet.

(However, I think Milton-san's suggestion is very desirable. 
 If preallocation of hotadd works on ia64 too, I'm very glad.)

Thanks.

-- 
Yasunori Goto 

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