Re: [PATCH] dax: Change return type to vm_fault_t

From: Randy Dunlap <rdunlap@infradead.org>
To: Souptick Joarder <jrdr.linux@gmail.com>,
	Dan Williams <dan.j.williams@intel.com>
Cc: Linux MM <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>,
	Matthew Wilcox <willy@infradead.org>,
	linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: Re: [PATCH] dax: Change return type to vm_fault_t
Date: Mon, 16 Apr 2018 11:41:27 -0700	[thread overview]
Message-ID: <79c1622b-71a3-a8f6-e814-3510ca0dc60e@infradead.org> (raw)
In-Reply-To: <CAFqt6zarE3N4Ha5w54ez9aGPDGh4Qr5uxcAfYnUYZUnzDb26yg@mail.gmail.com>

On 04/16/2018 11:37 AM, Souptick Joarder wrote:
> On Tue, Apr 17, 2018 at 12:05 AM, Dan Williams <dan.j.williams@intel.com> wrote:
>> On Mon, Apr 16, 2018 at 11:28 AM, Souptick Joarder <jrdr.linux@gmail.com> wrote:
>>> On Mon, Apr 16, 2018 at 11:51 PM, Matthew Wilcox <willy@infradead.org> wrote:
>>>> On Mon, Apr 16, 2018 at 11:00:26AM -0700, Dan Williams wrote:
>>>>> On Mon, Apr 16, 2018 at 10:47 AM, Matthew Wilcox <willy@infradead.org> wrote:
>>>>>> On Mon, Apr 16, 2018 at 09:14:48AM -0700, Dan Williams wrote:
>>>>>>>> -       rc = vm_insert_mixed(vmf->vma, vmf->address, pfn);
>>>>>>>> -
>>>>>>>> -       if (rc == -ENOMEM)
>>>>>>>> -               return VM_FAULT_OOM;
>>>>>>>> -       if (rc < 0 && rc != -EBUSY)
>>>>>>>> -               return VM_FAULT_SIGBUS;
>>>>>>>> -
>>>>>>>> -       return VM_FAULT_NOPAGE;
>>>>>>>> +       return vmf_insert_mixed(vmf->vma, vmf->address, pfn);
>>>>>>>
>>>>>>> Ugh, so this change to vmf_insert_mixed() went upstream without fixing
>>>>>>> the users? This changelog is now misleading as it does not mention
>>>>>>> that is now an urgent standalone fix. On first read I assumed this was
>>>>>>> part of a wider effort for 4.18.
>>>>>>
>>>>>> You read too quickly.  vmf_insert_mixed() is a *new* function which
>>>>>> *replaces* vm_insert_mixed() and
>>>>>> awful-mangling-of-return-values-done-per-driver.
>>>>>>
>>>>>> Eventually vm_insert_mixed() will be deleted.  But today is not that day.
>>>>>
>>>>> Ah, ok, thanks for the clarification. Then this patch should
>>>>> definitely be re-titled to "dax: convert to the new vmf_insert_mixed()
>>>>> helper". The vm_fault_t conversion is just a minor side-effect of that
>>>>> larger change. I assume this can wait for v4.18.
>>>
>>> The primary objective is to change the return type to
>>> vm_fault_t in all fault handlers and to support that
>>> we have replace vm_insert_mixed() with vmf_insert_
>>> mixed() within one fault handler function.
>>>
>>> Do I really need to change the patch title ?
>>
>> At this point, yes, or at least mention the vm_insert_mixed -->
>> vmf_insert_mixed conversion in the changelog.
> 
> Ok, I will add this in change log and send v2.
> 

and please try to use more columns per line of text.

E.g. from the uio: patch:

Use new return type vm_fault_t for fault handler
in struct vm_operations_struct. For now, this is
just documenting that the function returns a VM_
FAULT value rather than an errno.  Once all inst
ances are converted, vm_fault_t will become a di
stinct type

Several of those lines are chopped at odd places.

-- 
~Randy
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