linux-kernel - Re: [PATCH v5 2/2] dax/kmem: allow kmem to add memory with memmap_on

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Date:   Tue, 17 Oct 2023 13:18:56 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     "Verma, Vishal L" <vishal.l.verma@...el.com>
Cc:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "osalvador@...e.de" <osalvador@...e.de>,
        "david@...hat.com" <david@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "aneesh.kumar@...ux.ibm.com" <aneesh.kumar@...ux.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
        "Hocko, Michal" <mhocko@...e.com>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "jmoyer@...hat.com" <jmoyer@...hat.com>,
        "Jonathan.Cameron@...wei.com" <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v5 2/2] dax/kmem: allow kmem to add memory with
 memmap_on_memory

"Verma, Vishal L" <vishal.l.verma@...el.com> writes:

> On Thu, 2023-10-05 at 14:16 -0700, Dan Williams wrote:
>> Vishal Verma wrote:
>> >
> <..>
>
>> > +
>> > +       rc = kstrtobool(buf, &val);
>> > +       if (rc)
>> > +               return rc;
>>
>> Perhaps:
>>
>> if (dev_dax->memmap_on_memory == val)
>>         return len;
>>
>> ...and skip the check below when it is going to be a nop
>>
>> > +
>> > +       device_lock(dax_region->dev);
>> > +       if (!dax_region->dev->driver) {
>>
>> Is the polarity backwards here? I.e. if the device is already attached to
>> the kmem driver it is too late to modify memmap_on_memory policy.
>
> Hm this sounded logical until I tried it. After a reconfigure-device to
> devdax (i.e. detach kmem), I get the -EBUSY if I invert this check.

Can you try to unbind the device via sysfs by hand and retry?

--
Best Regards,
Huang, Ying

>>
>> > +               device_unlock(dax_region->dev);
>> > +               return -ENXIO;
>>

[snip]