linux-kernel - Re: [PATCH v2 2/5] mm: memory_hotplug: Remove assumption on memory state before hotremove

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Date:   Mon, 4 Dec 2017 15:05:05 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Andrea Reale <ar@...ux.vnet.ibm.com>
Cc:     joeyli <jlee@...e.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        m.bielski@...tualopensystems.com, arunks@....qualcomm.com,
        Mark Rutland <mark.rutland@....com>,
        scott.branden@...adcom.com, Will Deacon <will.deacon@....com>,
        qiuxishi@...wei.com, Catalin Marinas <catalin.marinas@....com>,
        Michal Hocko <mhocko@...e.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] mm: memory_hotplug: Remove assumption on memory
 state before hotremove

On Mon, Dec 4, 2017 at 12:28 PM, Andrea Reale <ar@...ux.vnet.ibm.com> wrote:
> Hi Joey,
>
> and thanks for your comments. Response inline:
>

[cut]

>>
>> So, the BUG() is useful to capture state issue in memory subsystem. But, I
>> understood your concern about the two steps offline/remove from userland.
>>
>> Maybe we should move the BUG() to somewhere but not just remove it. Or if
>> we think that the BUG() is too intense, at least we should print out a error
>> message, and ACPI should checks the return value from subsystem to
>> interrupt memory-hotplug process.
>
> In this patchset, BUG() is moved to acpi_memory_remove_memory(),
> the caller of arch_remove_memory(). However, I agree with Michal, that
> we should not BUG() here but rather halt the hotremove process and print
> some errors.
> Is there any state in ACPI that should be undone in case of hotremove
> errors or we can just stop the process "halfway"?

I have to recall a couple of things before answering this question, so
that may take some time.

Thanks,
Rafael