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From: Vlastimil Babka <vbabka@suse.cz>
To: Michal Hocko <mhocko@kernel.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
	Sachin Sant <sachinp@linux.vnet.ibm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Andrew Morton <akpm@linux-foundation.org>,
	linuxppc-dev@lists.ozlabs.org, Christopher Lameter <cl@linux.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Kirill Tkhai <ktkhai@virtuozzo.com>
Subject: Re: [PATCH 1/3] powerpc/numa: Set numa_node for all possible cpus
Date: Tue, 17 Mar 2020 14:44:45 +0100
Message-ID: <65b99db6-3bdf-6caa-74e5-6d6b681f16b5@suse.cz> (raw)
In-Reply-To: <20200316090652.GC11482@dhcp22.suse.cz>

On 3/16/20 10:06 AM, Michal Hocko wrote:
> On Thu 12-03-20 17:41:58, Vlastimil Babka wrote:
> [...]
>> with nid present in:
>> N_POSSIBLE - pgdat might not exist, node_to_mem_node() must return some online
> 
> I would rather have a dummy pgdat for those. Have a look at 
> $ git grep "NODE_DATA.*->" | wc -l
> 63
> 
> Who knows how many else we have there. I haven't looked more closely.
> Besides that what is a real reason to not have pgdat ther and force all
> users of a $random node from those that the platform considers possible
> for special casing? Is that a memory overhead? Is that really a thing?

I guess we can ignore memory overhead. I guess there only might be some concern
that for nodes that are initially offline, we will allocate the pgdat on a
different node, and after they are online, it will stay on a different node with
more access latency from local cpus. If we only allocate for online nodes, it
can always be local? But I guess it doesn't matter that much.

> Somebody has suggested to tweak some of the low level routines to do the
> special casing but I really have to say I do not like that. We shouldn't
> use the first online node or anything like that. We should simply always
> follow the topology presented by FW and of that we need to have a pgdat.
> 


  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-11 11:02 [PATCH 0/3] Offline memoryless cpuless node 0 Srikar Dronamraju
2020-03-11 11:02 ` [PATCH 1/3] powerpc/numa: Set numa_node for all possible cpus Srikar Dronamraju
2020-03-11 11:57   ` Michal Hocko
2020-03-12  5:27     ` Srikar Dronamraju
2020-03-12  8:23       ` Sachin Sant
2020-03-12  9:30         ` Vlastimil Babka
2020-03-12 13:14           ` Srikar Dronamraju
2020-03-12 13:51             ` Vlastimil Babka
2020-03-12 16:13               ` Srikar Dronamraju
2020-03-12 16:41                 ` Vlastimil Babka
2020-03-13  9:47                   ` Joonsoo Kim
2020-03-13 11:04                     ` Srikar Dronamraju
2020-03-13 11:38                       ` Vlastimil Babka
2020-03-16  8:15                         ` Joonsoo Kim
2020-03-13 11:22                   ` Srikar Dronamraju
2020-03-16  9:06                   ` Michal Hocko
2020-03-17 13:44                     ` Vlastimil Babka [this message]
2020-03-17 14:01                       ` Michal Hocko
2020-03-11 11:02 ` [PATCH 2/3] powerpc/numa: Prefer node id queried from vphn Srikar Dronamraju
2020-03-11 11:02 ` [PATCH 3/3] mm/page_alloc: Keep memoryless cpuless node 0 offline Srikar Dronamraju
2020-03-15 14:20   ` Christopher Lameter
2020-03-16  8:54     ` Michal Hocko
2020-03-18  7:50       ` Srikar Dronamraju
2020-03-18 18:57       ` Christopher Lameter

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