linux-kernel - Re: [PATCH 1/2] arm64: avoid alloc memory on offline node

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Message-ID: <87602d3ccl.fsf@e105922-lin.cambridge.arm.com>
Date:   Wed, 20 Jun 2018 12:51:22 +0100
From:   Punit Agrawal <punit.agrawal@....com>
To:     Xie XiuQi <xiexiuqi@...wei.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Michal Hocko <mhocko@...nel.org>,
        Hanjun Guo <guohanjun@...wei.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        <tnowicki@...iumnetworks.com>, <linux-pci@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Will Deacon <will.deacon@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        <linux-mm@...ck.org>, <wanghuiqiang@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        zhongjiang <zhongjiang@...wei.com>,
        linux-arm <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] arm64: avoid alloc memory on offline node

Xie XiuQi <xiexiuqi@...wei.com> writes:

> Hi Lorenzo, Punit,
>
>
> On 2018/6/20 0:32, Lorenzo Pieralisi wrote:
>> On Tue, Jun 19, 2018 at 04:35:40PM +0100, Punit Agrawal wrote:
>>> Michal Hocko <mhocko@...nel.org> writes:
>>>
>>>> On Tue 19-06-18 15:54:26, Punit Agrawal wrote:
>>>> [...]
>>>>> In terms of $SUBJECT, I wonder if it's worth taking the original patch
>>>>> as a temporary fix (it'll also be easier to backport) while we work on
>>>>> fixing these other issues and enabling memoryless nodes.
>>>>
>>>> Well, x86 already does that but copying this antipatern is not really
>>>> nice. So it is good as a quick fix but it would be definitely much
>>>> better to have a robust fix. Who knows how many other places might hit
>>>> this. You certainly do not want to add a hack like this all over...
>>>
>>> Completely agree! I was only suggesting it as a temporary measure,
>>> especially as it looked like a proper fix might be invasive.
>>>
>>> Another fix might be to change the node specific allocation to node
>>> agnostic allocations. It isn't clear why the allocation is being
>>> requested from a specific node. I think Lorenzo suggested this in one of
>>> the threads.
>> 
>> I think that code was just copypasted but it is better to fix the
>> underlying issue.
>> 
>>> I've started putting together a set fixing the issues identified in this
>>> thread. It should give a better idea on the best course of action.
>> 
>> On ACPI ARM64, this diff should do if I read the code correctly, it
>> should be (famous last words) just a matter of mapping PXMs to nodes for
>> every SRAT GICC entry, feel free to pick it up if it works.
>> 
>> Yes, we can take the original patch just because it is safer for an -rc
>> cycle even though if the patch below would do delaying the fix for a
>> couple of -rc (to get it tested across ACPI ARM64 NUMA platforms) is
>> not a disaster.
>
> I tested this patch on my arm board, it works.

I am assuming you tried the patch without enabling support for
memory-less nodes.

The patch de-couples the onlining of numa nodes (as parsed from SRAT)
from NR_CPUS restriction. When it comes to building zonelists, the node
referenced by the PCI controller also has zonelists initialised.

So it looks like a fallback node is setup even if we don't have
memory-less nodes enabled. I need to stare some more at the code to see
why we need memory-less nodes at all then ...