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Subject: Re: [PATCH v2 02/11] mm/hmm: use reference counting for HMM struct v2
To:     Jerome Glisse <jglisse@redhat.com>
CC:     Ira Weiny <ira.weiny@intel.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
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From:   John Hubbard <jhubbard@nvidia.com>
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On 3/28/19 2:21 PM, Jerome Glisse wrote:
> On Thu, Mar 28, 2019 at 01:43:13PM -0700, John Hubbard wrote:
>> On 3/28/19 12:11 PM, Jerome Glisse wrote:
>>> On Thu, Mar 28, 2019 at 04:07:20AM -0700, Ira Weiny wrote:
>>>> On Mon, Mar 25, 2019 at 10:40:02AM -0400, Jerome Glisse wrote:
>>>>> From: J=C3=A9r=C3=B4me Glisse <jglisse@redhat.com>
[...]
>>>>> @@ -67,14 +78,9 @@ struct hmm {
>>>>>   */
>>>>>  static struct hmm *hmm_register(struct mm_struct *mm)
>>>>>  {
>>>>> -	struct hmm *hmm =3D READ_ONCE(mm->hmm);
>>>>> +	struct hmm *hmm =3D mm_get_hmm(mm);
>>>>
>>>> FWIW: having hmm_register =3D=3D "hmm get" is a bit confusing...
>>>
>>> The thing is that you want only one hmm struct per process and thus
>>> if there is already one and it is not being destroy then you want to
>>> reuse it.
>>>
>>> Also this is all internal to HMM code and so it should not confuse
>>> anyone.
>>>
>>
>> Well, it has repeatedly come up, and I'd claim that it is quite=20
>> counter-intuitive. So if there is an easy way to make this internal=20
>> HMM code clearer or better named, I would really love that to happen.
>>
>> And we shouldn't ever dismiss feedback based on "this is just internal
>> xxx subsystem code, no need for it to be as clear as other parts of the
>> kernel", right?
>=20
> Yes but i have not seen any better alternative that present code. If
> there is please submit patch.
>=20

Ira, do you have any patch you're working on, or a more detailed suggestion=
 there?
If not, then I might (later, as it's not urgent) propose a small cleanup pa=
tch=20
I had in mind for the hmm_register code. But I don't want to duplicate effo=
rt=20
if you're already thinking about it.


thanks,
--=20
John Hubbard
NVIDIA