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Date: Thu, 27 Mar 2008 19:51:26 -0700 From: Jeremy Fitzhardinge <jeremy@...p.org> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> 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 KAMEZAWA Hiroyuki wrote: > 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. > Yes. That's why I added add_memory_resource(), so I could use allocate_resource() to find a non-overlapping range to put the new memory. > (I wrote online_page() in above, but online_pages() is maybe better. > It does all what you want.) > No, for my use-case the pages must be onlined one by one as they get some physical memory assigned to them. At the time I do add_memory(), I'm just allocating page structures, but there's no memory backing that range. That's why I need to disable the sysfs onlining interface, because it bulk onlines the pages before there's anything behind them. > 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. > I'd really rather prevent online_pages from happening at all, since it can only cause havoc. Thanks, J -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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