linux-kernel - Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM

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Date:   Wed, 13 Feb 2019 14:06:59 +0100
From:   Brice Goglin <Brice.Goglin@...ia.fr>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Michal Hocko <mhocko@...e.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Takashi Iwai <tiwai@...e.de>,
        Ross Zwisler <zwisler@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Yaowei Bai <baiyaowei@...s.chinamobile.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal
 RAM


Le 13/02/2019 à 09:43, Brice Goglin a écrit :
> Le 13/02/2019 à 09:24, Dan Williams a écrit :
>> On Wed, Feb 13, 2019 at 12:12 AM Brice Goglin <Brice.Goglin@...ia.fr> wrote:
>>> Le 13/02/2019 à 01:30, Dan Williams a écrit :
>>>> On Tue, Feb 12, 2019 at 11:59 AM Brice Goglin <Brice.Goglin@...ia.fr> wrote:
>>>>> # ndctl disable-region all
>>>>> # ndctl zero-labels all
>>>>> # ndctl enable-region region0
>>>>> # ndctl create-namespace -r region0 -t pmem -m devdax
>>>>> {
>>>>>   "dev":"namespace0.0",
>>>>>   "mode":"devdax",
>>>>>   "map":"dev",
>>>>>   "size":"1488.37 GiB (1598.13 GB)",
>>>>>   "uuid":"ad0096d7-3fe7-4402-b529-ad64ed0bf789",
>>>>>   "daxregion":{
>>>>>     "id":0,
>>>>>     "size":"1488.37 GiB (1598.13 GB)",
>>>>>     "align":2097152,
>>>>>     "devices":[
>>>>>       {
>>>>>         "chardev":"dax0.0",
>>>>>         "size":"1488.37 GiB (1598.13 GB)"
>>>>>       }
>>>>>     ]
>>>>>   },
>>>>>   "align":2097152
>>>>> }
>>>>> # ndctl enable-namespace namespace0.0
>>>>> # echo -n dax0.0 > /sys/bus/dax/drivers/device_dax/remove_id
>>>>> <hang>
>>>>>
>>>>> I tried with and without dax_pmem_compat loaded, but it doesn't help.
>>>> I think this is due to:
>>>>
>>>>   a9f1ffdb6a20 device-dax: Auto-bind device after successful new_id
>>>>
>>>> I missed that this path is also called in the remove_id path. Thanks
>>>> for the bug report! I'll get this fixed up.
>>> Now that remove_id is fixed, things fails later in Dave's procedure:
>>>
>>> # echo -n dax0.0 > /sys/bus/dax/drivers/device_dax/remove_id
>>> # echo -n dax0.0 > /sys/bus/dax/drivers/device_dax/unbind
>>> # echo -n dax0.0 > /sys/bus/dax/drivers/kmem/new_id
>> In the current version of the code the bind is not necessary, so the
>> lack of error messages here means the bind succeeded.


It looks like "unbind" is required to make the PMEM appear as a new
node. If I remove_id from devdax and new_id to kmem without "unbind" in
the middle, nothing appears.

Writing to "kmem/bind" didn't seem necessary.

Brice



>>
>>> # echo -n dax0.0 > /sys/bus/dax/drivers/kmem/bind
>>> -bash: echo: write error: No such device
>> This also happens when the device is already bound.
>>
>>> (And nothing seems to have changed in /sys/devices/system/memory/*/state)
>> What does "cat /proc/iomem" say?
>
> 3060000000-1aa5fffffff : Persistent Memory
>   3060000000-36481fffff : namespace0.0
>   3680000000-1a9ffffffff : dax0.0
>     3680000000-1a9ffffffff : System RAM
> (the last line wasn't here before attaching to kmem)
>
> I said nothing changed in memory/*/state, I actually meant that nothing
> was offline. But things are actually working!
>
> First, node4 appeared, all memory is already attached to it without
> having to write to memory/*/state
>
> Node 4 MemTotal:       1558183936 kB
> Node 4 MemFree:        1558068564 kB
> Node 4 MemUsed:          115372 kB
>
> I wasn't expecting node4 to appear because the machine has no
> /sys/firmware/acpi/tables/HMAT when running in 1LM (there's one in 2LM).
> I thought you said in the past that no HMAT would mean memory would be
> added to the existing DDR node?
>
> Thanks!
>
> Brice
>
>