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

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Date:   Wed, 13 Feb 2019 00:24:04 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Brice Goglin <Brice.Goglin@...ia.fr>
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

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.

> # 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?