linux-kernel - Re: [PATCH 4/6] Have x86_64 use add_active_range() and free_area_init

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Date:	Thu, 31 Aug 2006 20:40:59 +0300
From:	Mika Penttilä <mika.penttila@...umbus.fi>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Keith Mannthey <kmannth@...il.com>, akpm@...l.org,
	tony.luck@...el.com,
	Linux Memory Management List <linux-mm@...ck.org>,
	ak@...e.de, bob.picco@...com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] Have x86_64 use add_active_range() and free_area_init_nodes

Mel Gorman wrote:
> On Thu, 31 Aug 2006, Mika Penttilä wrote:
>
>>
>>>>> static __init inline int srat_disabled(void)
>>>>> @@ -166,7 +167,7 @@ static int hotadd_enough_memory(struct b
>>>>>
>>>>>        if (mem < 0)
>>>>>                return 0;
>>>>> -       allowed = (end_pfn - e820_hole_size(0, end_pfn)) * PAGE_SIZE;
>>>>> +       allowed = (end_pfn - absent_pages_in_range(0, end_pfn)) * 
>>>>> PAGE_SIZE;
>>>>>        allowed = (allowed / 100) * hotadd_percent;
>>>>>        if (allocated + mem > allowed) {
>>>>>                unsigned long range;
>>>>> @@ -238,7 +239,7 @@ static int reserve_hotadd(int node, unsi
>>>>>        }
>>>>>
>>>>>        /* This check might be a bit too strict, but I'm keeping it 
>>>>> for now. */
>>>>> -       if (e820_hole_size(s_pfn, e_pfn) != e_pfn - s_pfn) {
>>>>> +       if (absent_pages_in_range(s_pfn, e_pfn) != e_pfn - s_pfn) {
>>>>>                printk(KERN_ERR "SRAT: Hotplug area has existing 
>>>>> memory\n");
>>>>>                return -1;
>>>>>        }
>>>>>
>>>> We really do want to to compare against the e820 map at it contains
>>>> the memory that is really present (this info was blown away before
>>>> acpi_numa) 
>>>
>>> The information used by absent_pages_in_range() should match what was
>>> available to e820_hole_size().
>>>
>>>
>> But it doesn't : all active ranges are removed before parsing srat. I 
>> think we really need to check against e820 here.
>>
>
> What I see happening is this;
>
> 1. setup_arch calls e820_register_active_regions(0, 0, -1UL) so that all
>    regions are registered as if they were on node 0 so e820_end_of_ram()
>    gets the right value
> 2. remove_all_active_regions() is called to clear what was registered so
>    that rediscovery with NUMA awareness happens
> 3. acpi_numa_init() is called. It parses the table and a little later
>    calls acpi_numa_memory_affinity_init() for each range in the table so
>    now we're into x86_64 code
> 4. acpi_numa_memory_affinity_init() basically deals an address range.
>    Assuming the SRAT table is not broken, it calls
>    e820_register_active_ranges() for that range. At this point, for the
>    range of addresses, the active ranges are now registered
> 5. reserve_hotadd is called if the range is hotpluggable. It will fail if
>    it finds that memory already exists there
>
> So, when absent_pages_in_range() is being called by reserve_hotadd(), 
> it should be using the same information that was available in e820. 
> What am I missing?
>
Ok, right, missed the e820_register_active_ranges() in 
acpi_numa_memory_affinity_init() before reserve_hotadd stuff. So 
logically it should be working mod bugs.

Argh, just looked through the reserve hotadd code and 
hotadd_enough_memory() looks still broken. And why are we doing 
reserve_bootmem_node(), the regions aren't present RAM anyways?

--Mika

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