linux-kernel - Re: [PATCH] mm/alloc: fallback to first node if the wanted node offline

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Message-ID: <ffd7160c-b5dc-364f-a5cd-ac3f16181ced@suse.cz>
Date:   Tue, 4 Dec 2018 15:42:08 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>,
        Pingfan Liu <kernelfans@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH] mm/alloc: fallback to first node if the wanted node
 offline

On 12/4/18 9:56 AM, Michal Hocko wrote:
>> The device's node num is 2. And in my case, I used nr_cpus param. Due
>> to init_cpu_to_node() initialize all the possible node.  It is hard
>> for me to figure out without this param, how zonelists is accessed
>> before page allocator works.
> I believe we should focus on this. Why does the node have no zonelist
> even though all zonelists should be initialized already? Maybe this is
> nr_cpus pecularity and we do not initialize all the existing numa nodes.
> Or maybe the device is associated to a non-existing node with that
> setup. A full dmesg might help us here.

Yes, a full dmesg should contain line such as this one:

[    0.137407] Built 1 zonelists, mobility grouping on.  Total pages:
6181664

That should at least tell us if nr_cpus=X resulted in some node's
zonelists not being built.