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

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Message-Id: <20080328113312.65cca8b5.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 28 Mar 2008 11:33:12 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Yasunori Goto <y-goto@...fujitsu.com>, 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 19:13:20 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> >> 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?
> 
Maybe no. but be carefull not to register resource in overlapped manner.
(I wrote online_page() in above, but online_pages() is maybe better.
 It does all what you want.)

Start/Size are automatically alined to section in __add_pages().

See below.
==
110 int __add_pages(struct zone *zone, unsigned long phys_start_pfn,
 111                  unsigned long nr_pages)
 112 {
 113         unsigned long i;
 114         int err = 0;
 115         int start_sec, end_sec;
 116         /* during initialize mem_map, align hot-added range to section */
 117         start_sec = pfn_to_section_nr(phys_start_pfn);
 118         end_sec = pfn_to_section_nr(phys_start_pfn + nr_pages - 1);
==

And online_pages(), which onlines pages in [pfn, pfn + size), will see
registerred resources within [pfn, pfn + size).
==
184 int online_pages(unsigned long pfn, unsigned long nr_pages)
<snip>
227         walk_memory_resource(pfn, nr_pages, &onlined_pages,
228                 online_pages_range);
==

One of my concern is how-to-handle sysfs status in this case.

Another concerns is, currently, I think no one tried to online a section twice
to online reserved pages in a section. so, you may see bug.
For example, mem_notify() in online_pages() will be called several times against
a section.

Thanks,
-Kame


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