Date:	Mon, 11 Sep 2006 22:44:51 +0100
From:	Andy Whitcroft <apw@...dowen.org>
To:	kmannth@...ibm.com
CC:	linux-mm <linux-mm@...ck.org>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] patch[1/1] i386 numa kva conversion to use bootmem	reserve

keith mannthey wrote:
> On Sun, 2006-09-10 at 03:41 +0100, Andy Whitcroft wrote:
>> keith mannthey wrote:
>>> Hello,
>>>   I the current i386 numa the numa_kva (the area used to remap node
>>> local data in lowmem) space is acquired by adjusting the end of low
>>> memroy during boot. 
>>>
>>> (from setup_memory)
>>> reserve_pages = calculate_numa_remap_pages();
>>> (then)
>>> system_max_low_pfn = max_low_pfn = find_max_low_pfn() - reserve_pages;
>>>
>>> The problem this is that initrds can be trampled over (the kva can
>>> adjust system_max_low_pfn into the initrd area) This results in kernel
>>> throwing away the intird and a failed boot.  This is a long standing
>>> issue. (It has been like this at least for the last few years). 
>>>
>>> This patch keeps the numa kva code from adjusting the end of memory and
>>> coverts it is just use the reserve_bootmem call to reserve the large
>>> amount of space needed for the numa_kva. It is mindful of initrds when
>>> present. 
>>>
>>> This patch was built against 2.6.17-rc1 originally but applies and boots
>>> against 2.6.17 just fine.  I have only test this against the summit
>>> subarch (I don't have other i386 numa hw). 
>>>
>>> all feedback welcome!
>>>
>>> Signed-off-by:  Keith Mannthey <kmannth@...ibm.com>
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
>>> diff -urN linux-2.6.17/arch/i386/kernel/setup.c linux-2.6.17-work/arch/i386/kernel/setup.c
>>> --- linux-2.6.17/arch/i386/kernel/setup.c	2006-06-17 18:49:35.000000000 -0700
>>> +++ linux-2.6.17-work/arch/i386/kernel/setup.c	2006-06-20 23:04:37.000000000 -0700
>>> @@ -1210,6 +1210,9 @@
>>>  extern void zone_sizes_init(void);
>>>  #endif /* !CONFIG_NEED_MULTIPLE_NODES */
>>>  
>>> +#ifdef CONFIG_NUMA
>>> +extern void numa_kva_reserve(void);
>>> +#endif
>>>  void __init setup_bootmem_allocator(void)
>>>  {
>>>  	unsigned long bootmap_size;
>>> @@ -1265,7 +1268,9 @@
>>>  	 */
>>>  	find_smp_config();
>>>  #endif
>>> -
>>> +#ifdef CONFIG_NUMA
>>> +	numa_kva_reserve();
>>> +#endif 
>>>  #ifdef CONFIG_BLK_DEV_INITRD
>>>  	if (LOADER_TYPE && INITRD_START) {
>>>  		if (INITRD_START + INITRD_SIZE <= (max_low_pfn << PAGE_SHIFT)) {
>>> diff -urN linux-2.6.17/arch/i386/mm/discontig.c linux-2.6.17-work/arch/i386/mm/discontig.c
>>> --- linux-2.6.17/arch/i386/mm/discontig.c	2006-06-17 18:49:35.000000000 -0700
>>> +++ linux-2.6.17-work/arch/i386/mm/discontig.c	2006-06-20 23:11:49.000000000 -0700
>>> @@ -118,7 +118,8 @@
>>>  
>>>  void *node_remap_end_vaddr[MAX_NUMNODES];
>>>  void *node_remap_alloc_vaddr[MAX_NUMNODES];
>>> -
>>> +static unsigned long kva_start_pfn;
>>> +static unsigned long kva_pages;
>>>  /*
>>>   * FLAT - support for basic PC memory model with discontig enabled, essentially
>>>   *        a single node with all available processors in it with a flat
>>> @@ -287,7 +288,6 @@
>>>  {
>>>  	int nid;
>>>  	unsigned long system_start_pfn, system_max_low_pfn;
>>> -	unsigned long reserve_pages;
>>>  
>>>  	/*
>>>  	 * When mapping a NUMA machine we allocate the node_mem_map arrays
>>> @@ -299,14 +299,23 @@
>>>  	find_max_pfn();
>>>  	get_memcfg_numa();
>>>  
>>> -	reserve_pages = calculate_numa_remap_pages();
>>> +	kva_pages = calculate_numa_remap_pages();
>>>  
>>>  	/* partially used pages are not usable - thus round upwards */
>>>  	system_start_pfn = min_low_pfn = PFN_UP(init_pg_tables_end);
>>>  
>>> -	system_max_low_pfn = max_low_pfn = find_max_low_pfn() - reserve_pages;
>>> -	printk("reserve_pages = %ld find_max_low_pfn() ~ %ld\n",
>>> -			reserve_pages, max_low_pfn + reserve_pages);
>>> +	kva_start_pfn = find_max_low_pfn() - kva_pages;
>>> +
>>> +#ifdef CONFIG_BLK_DEV_INITRD
>>> +	/* Numa kva area is below the initrd */
>>> +	if (LOADER_TYPE && INITRD_START) 
>>> +		kva_start_pfn = PFN_DOWN(INITRD_START)  - kva_pages;
>>> +#endif 
>>> +	kva_start_pfn -= kva_start_pfn & (PTRS_PER_PTE-1);
>>> +
>>> +	system_max_low_pfn = max_low_pfn = find_max_low_pfn();
>>> +	printk("kva_start_pfn ~ %ld find_max_low_pfn() ~ %ld\n", 
>>> +		kva_start_pfn, max_low_pfn);
>>>  	printk("max_pfn = %ld\n", max_pfn);
>>>  #ifdef CONFIG_HIGHMEM
>>>  	highstart_pfn = highend_pfn = max_pfn;
>>> @@ -324,7 +333,7 @@
>>>  			(ulong) pfn_to_kaddr(max_low_pfn));
>>>  	for_each_online_node(nid) {
>>>  		node_remap_start_vaddr[nid] = pfn_to_kaddr(
>>> -				highstart_pfn + node_remap_offset[nid]);
>>> +				kva_start_pfn + node_remap_offset[nid]);
>>>  		/* Init the node remap allocator */
>>>  		node_remap_end_vaddr[nid] = node_remap_start_vaddr[nid] +
>>>  			(node_remap_size[nid] * PAGE_SIZE);
>>> @@ -339,7 +348,6 @@
>>>  	}
>>>  	printk("High memory starts at vaddr %08lx\n",
>>>  			(ulong) pfn_to_kaddr(highstart_pfn));
>>> -	vmalloc_earlyreserve = reserve_pages * PAGE_SIZE;
>>>  	for_each_online_node(nid)
>>>  		find_max_pfn_node(nid);
>>>  
>>> @@ -349,6 +357,12 @@
>>>  	return max_low_pfn;
>>>  }
>>>  
>>> +void __init numa_kva_reserve (void) 
>>> +{
>>> +	reserve_bootmem(PFN_PHYS(kva_start_pfn),PFN_PHYS(kva_pages));
>>> +
>>> +}
>>> +
>>>  void __init zone_sizes_init(void)
>>>  {
>>>  	int nid;
>> The primary reason that the mem_map is cut from the end of ZONE_NORMAL
>> is so that memory that would back that stolen KVA gets pushed out into
>> ZONE_HIGHMEM, the boundary between them is moved down.  By using
>> reserve_bootmem we will mark the pages which are currently backing the
>> KVA you are 'reusing' as reserved and prevent their release; we pay
>> double for the mem_map.
> 
> Perhaps just freeing the reserve pages and remapping them at an
> appropriate time could accomplish this?  Sorry I don't know the KVA
> "freeing" path can you describe it a little more?  When are these pages
> returned to the system?  It was my understanding that that KVA pages
> were lost (the original wayu shrinks ZONE_NORMAL and creates a hole
> between the zones).


No it does seem like we loose the memory at the end of NORMAL when we
shrink it, but really happens is we move the boundary down. Any page
above the boundary is then in HIGHMEM and available to be allocated.
> 
>> If the initrd's are falling into this space, can we not allocate some
>> bootmem for those and move them out of our way?  As filesystem images
>> they are essentially location neutral so this should be safe?
> 
> AFAIK bootloaders choose where map initrds.  Grub seems to put it around
> the top of ZONE_NORMAL but it is pretty free to map it where it wants. I
> suppose INITRD_START INITRD_END and all that could be dynamic and moved
> around a bit but it seems a little messy. I would rather see the special
> case (i386 numa the rare beast it is) jump thought a few extra hoops
> than to muck with the initrd code. 

Right we can't change where grub puts it.  But doesn't it tell us where
it is as part of the kernel parameterisation.  That would allow us to
move it out of our way and change the parameters to that new location,
allowing normal processing to find it in the new location.

Be interested to see the layout during boot on one of these boxes :).

-apw
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