linux-kernel - Re: [PATCH v3 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER

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Date:   Thu, 2 Apr 2020 21:46:05 -0700
From:   Hoan Tran <hoan@...amperecomputing.com>
To:     Baoquan He <bhe@...hat.com>, Michal Hocko <mhocko@...nel.org>
Cc:     Mike Rapoport <rppt@...ux.ibm.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Oscar Salvador <osalvador@...e.de>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "David S. Miller" <davem@...emloft.net>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
        sparclinux@...r.kernel.org, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        lho@...erecomputing.com, mmorana@...erecomputing.com
Subject: Re: [PATCH v3 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by
 default for NUMA

Hi All,

On 3/31/20 7:31 AM, Baoquan He wrote:
> On 03/31/20 at 04:21pm, Michal Hocko wrote:
>> On Tue 31-03-20 22:03:32, Baoquan He wrote:
>>> Hi Michal,
>>>
>>> On 03/31/20 at 10:55am, Michal Hocko wrote:
>>>> On Tue 31-03-20 11:14:23, Mike Rapoport wrote:
>>>>> Maybe I mis-read the code, but I don't see how this could happen. In the
>>>>> HAVE_MEMBLOCK_NODE_MAP=y case, free_area_init_node() calls
>>>>> calculate_node_totalpages() that ensures that node->node_zones are entirely
>>>>> within the node because this is checked in zone_spanned_pages_in_node().
>>>>
>>>> zone_spanned_pages_in_node does chech the zone boundaries are within the
>>>> node boundaries. But that doesn't really tell anything about other
>>>> potential zones interleaving with the physical memory range.
>>>> zone->spanned_pages simply gives the physical range for the zone
>>>> including holes. Interleaving nodes are essentially a hole
>>>> (__absent_pages_in_range is going to skip those).
>>>>
>>>> That means that when free_area_init_core simply goes over the whole
>>>> physical zone range including holes and that is why we need to check
>>>> both for physical and logical holes (aka other nodes).
>>>>
>>>> The life would be so much easier if the whole thing would simply iterate
>>>> over memblocks...
>>>
>>> The memblock iterating sounds a great idea. I tried with putting the
>>> memblock iterating in the upper layer, memmap_init(), which is used for
>>> boot mem only anyway. Do you think it's doable and OK? It yes, I can
>>> work out a formal patch to make this simpler as you said. The draft code
>>> is as below. Like this it uses the existing code and involves little change.
>>
>> Doing this would be a step in the right direction! I haven't checked the
>> code very closely though. The below sounds way too simple to be truth I
>> am afraid. First for_each_mem_pfn_range is available only for
>> CONFIG_HAVE_MEMBLOCK_NODE_MAP (which is one of the reasons why I keep
>> saying that I really hate that being conditional). Also I haven't really
>> checked the deferred initialization path - I have a very vague
>> recollection that it has been converted to the memblock api but I have
>> happilly dropped all that memory.
> 
> Thanks for your quick response and pointing out the rest suspect aspects,
> I will investigate what you mentioned, see if they impact.

I would like to check if we still move on with my patch to remove 
CONFIG_NODES_SPAN_OTHER_NODES and have another patch on top it?

Thanks
Hoan

> 
>>   
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 138a56c0f48f..558d421f294b 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -6007,14 +6007,6 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>>>   		 * function.  They do not exist on hotplugged memory.
>>>   		 */
>>>   		if (context == MEMMAP_EARLY) {
>>> -			if (!early_pfn_valid(pfn)) {
>>> -				pfn = next_pfn(pfn);
>>> -				continue;
>>> -			}
>>> -			if (!early_pfn_in_nid(pfn, nid)) {
>>> -				pfn++;
>>> -				continue;
>>> -			}
>>>   			if (overlap_memmap_init(zone, &pfn))
>>>   				continue;
>>>   			if (defer_init(nid, pfn, end_pfn))
>>> @@ -6130,9 +6122,17 @@ static void __meminit zone_init_free_lists(struct zone *zone)
>>>   }
>>>   
>>>   void __meminit __weak memmap_init(unsigned long size, int nid,
>>> -				  unsigned long zone, unsigned long start_pfn)
>>> +				  unsigned long zone, unsigned long range_start_pfn)
>>>   {
>>> -	memmap_init_zone(size, nid, zone, start_pfn, MEMMAP_EARLY, NULL);
>>> +	unsigned long start_pfn, end_pfn;
>>> +	unsigned long range_end_pfn = range_start_pfn + size;
>>> +	int i;
>>> +	for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) {
>>> +		start_pfn = clamp(start_pfn, range_start_pfn, range_end_pfn);
>>> +		end_pfn = clamp(end_pfn, range_start_pfn, range_end_pfn);
>>> +		if (end_pfn > start_pfn)
>>> +			memmap_init_zone(size, nid, zone, start_pfn, MEMMAP_EARLY, NULL);
>>> +	}
>>>   }
>>>   
>>>   static int zone_batchsize(struct zone *zone)
>>
>> -- 
>> Michal Hocko
>> SUSE Labs
>>
>