Re: [PATCH v3 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA

From: Hoan Tran <hoan@os.amperecomputing.com>
To: Baoquan He <bhe@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Oscar Salvador <osalvador@suse.de>,
	Pavel Tatashin <pavel.tatashin@microsoft.com>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"David S. Miller" <davem@davemloft.net>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
	linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org,
	sparclinux@vger.kernel.org, x86@kernel.org,
	linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
	lho@amperecomputing.com, mmorana@amperecomputing.com
Subject: Re: [PATCH v3 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA
Date: Fri, 3 Apr 2020 09:36:10 -0700	[thread overview]
Message-ID: <419b415c-6e34-cb87-88bc-f17f03acffcb@os.amperecomputing.com> (raw)
In-Reply-To: <20200403070904.GO2402@MiWiFi-R3L-srv>

Hi,

On 4/3/20 12:09 AM, Baoquan He wrote:
> On 04/02/20 at 09:46pm, Hoan Tran wrote:
>> 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?
> 
> I think we would like to replace CONFIG_NODES_SPAN_OTHER_NODES with
> CONFIG_NUMA, and just let UMA return 0 as node id, as Michal replied in
> another mail. Anyway, your patch 2~5 are still needed to sit on top of
> the change of this new plan.

Got it. Thanks for quick response.

Regards
Hoan
> 