linux-kernel - Re: [PATCH 2/5] mm/resource: move HMM pr

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Date:   Fri, 25 Jan 2019 13:24:43 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>, zwisler@...nel.org,
        vishal.l.verma@...el.com, thomas.lendacky@....com,
        Andrew Morton <akpm@...ux-foundation.org>, mhocko@...e.com,
        linux-nvdimm@...ts.01.org, linux-mm@...ck.org,
        Huang Ying <ying.huang@...el.com>,
        Wu Fengguang <fengguang.wu@...el.com>,
        Jerome Glisse <jglisse@...hat.com>
Subject: Re: [PATCH 2/5] mm/resource: move HMM pr_debug() deeper into resource
 code

On 1/25/19 1:18 PM, Bjorn Helgaas wrote:
> On Thu, Jan 24, 2019 at 5:21 PM Dave Hansen <dave.hansen@...ux.intel.com> wrote:
>> diff -puN kernel/resource.c~move-request_region-check kernel/resource.c
>> --- a/kernel/resource.c~move-request_region-check       2019-01-24 15:13:14.453199539 -0800
>> +++ b/kernel/resource.c 2019-01-24 15:13:14.458199539 -0800
>> @@ -1123,6 +1123,16 @@ struct resource * __request_region(struc
>>                 conflict = __request_resource(parent, res);
>>                 if (!conflict)
>>                         break;
>> +               /*
>> +                * mm/hmm.c reserves physical addresses which then
>> +                * become unavailable to other users.  Conflicts are
>> +                * not expected.  Be verbose if one is encountered.
>> +                */
>> +               if (conflict->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY) {
>> +                       pr_debug("Resource conflict with unaddressable "
>> +                                "device memory at %#010llx !\n",
>> +                                (unsigned long long)start);
> 
> I don't object to the change, but are you really OK with this being a
> pr_debug() message that is only emitted when enabled via either the
> dynamic debug mechanism or DEBUG being defined?  From the comments, it
> seems more like a KERN_INFO sort of message.

I left it consistent with the original message that was in the code.
I'm happy to change it, though, if the consumers of it (Jerome,
basically) want something different.

> Also, maybe the message would be more useful if it included the
> conflicting resource as well as the region you're requesting?  Many of
> the other callers of request_resource_conflict() have something like
> this:
> 
>   dev_err(dev, "resource collision: %pR conflicts with %s %pR\n",
>         new, conflict->name, conflict);

Seems sane.  I was just trying to change as little as possible.