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

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Message-ID: <419b415c-6e34-cb87-88bc-f17f03acffcb@os.amperecomputing.com>
Date:   Fri, 3 Apr 2020 09:36:10 -0700
From:   Hoan Tran <hoan@...amperecomputing.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        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,


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
>