From: John Hubbard <jhubbard@nvidia.com>
To: Jerome Glisse <jglisse@redhat.com>, Ira Weiny <ira.weiny@intel.com>
Cc: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v2 02/11] mm/hmm: use reference counting for HMM struct v2
Date: Fri, 29 Mar 2019 13:07:45 -0700 [thread overview]
Message-ID: <144f034d-9688-5aad-7b68-34e1d4b08228@nvidia.com> (raw)
In-Reply-To: <20190329022519.GJ16680@redhat.com>
On 3/28/19 7:25 PM, Jerome Glisse wrote:
[...]
>> The input value is not the problem. The problem is in the naming.
>>
>> obj = get_obj( various parameters );
>> put_obj(obj);
>>
>>
>> The problem is that the function is named hmm_register() either "gets" a
>> reference to _or_ creates and gets a reference to the hmm object.
>>
>> What John is probably ready to submit is something like.
>>
>> struct hmm *get_create_hmm(struct mm *mm);
>> void put_hmm(struct hmm *hmm);
>>
>>
>> So when you are reading the code you see...
>>
>> foo(...) {
>> struct hmm *hmm = get_create_hmm(mm);
>>
>> if (!hmm)
>> error...
>>
>> do stuff...
>>
>> put_hmm(hmm);
>> }
>>
>> Here I can see a very clear get/put pair. The name also shows that the hmm is
>> created if need be as well as getting a reference.
>>
>
> You only need to create HMM when you either register a mirror or
> register a range. So they two pattern:
>
> average_foo() {
> struct hmm *hmm = mm_get_hmm(mm);
> ...
> hmm_put(hmm);
> }
>
> register_foo() {
> struct hmm *hmm = hmm_register(mm);
> ...
> return 0;
> error:
> ...
> hmm_put(hmm);
> }
>
1. Looking at this fresh this morning, Ira's idea of just a single rename
actually clarifies things a lot more than I expected. I think the following
tiny patch would suffice here (I've updated documentation to match, and added
a missing "@Return:" line too):
iff --git a/mm/hmm.c b/mm/hmm.c
index fd143251b157..37b1c5803f1e 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -50,14 +50,17 @@ static inline struct hmm *mm_get_hmm(struct mm_struct *mm)
}
/*
- * hmm_register - register HMM against an mm (HMM internal)
+ * hmm_get_create - returns an HMM object, either by referencing the existing
+ * (per-process) object, or by creating a new one.
*
- * @mm: mm struct to attach to
+ * @mm: the mm_struct to attach to
+ * @Return: a pointer to the HMM object, or NULL upon failure. This pointer must
+ * be released, when done, via hmm_put().
*
- * This is not intended to be used directly by device drivers. It allocates an
- * HMM struct if mm does not have one, and initializes it.
+ * This is an internal HMM function, and is not intended to be used directly by
+ * device drivers.
*/
-static struct hmm *hmm_register(struct mm_struct *mm)
+static struct hmm *hmm_get_create(struct mm_struct *mm)
{
struct hmm *hmm = mm_get_hmm(mm);
bool cleanup = false;
@@ -288,7 +291,7 @@ int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
if (!mm || !mirror || !mirror->ops)
return -EINVAL;
- mirror->hmm = hmm_register(mm);
+ mirror->hmm = hmm_get_create(mm);
if (!mirror->hmm)
return -ENOMEM;
@@ -915,7 +918,7 @@ int hmm_range_register(struct hmm_range *range,
range->start = start;
range->end = end;
- range->hmm = hmm_register(mm);
+ range->hmm = hmm_get_create(mm);
if (!range->hmm)
return -EFAULT;
2. A not directly related point: did you see my minor comment on patch 0001? I think it might have been missed in all the threads yesterday.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2019-03-29 20:07 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-25 14:40 [PATCH v2 00/11] Improve HMM driver API v2 jglisse
2019-03-25 14:40 ` [PATCH v2 01/11] mm/hmm: select mmu notifier when selecting HMM jglisse
2019-03-28 20:33 ` John Hubbard
2019-03-29 21:15 ` Jerome Glisse
2019-03-29 21:42 ` John Hubbard
2019-03-25 14:40 ` [PATCH v2 02/11] mm/hmm: use reference counting for HMM struct v2 jglisse
2019-03-28 11:07 ` Ira Weiny
2019-03-28 19:11 ` Jerome Glisse
2019-03-28 20:43 ` John Hubbard
2019-03-28 21:21 ` Jerome Glisse
2019-03-29 0:39 ` John Hubbard
2019-03-28 16:57 ` Ira Weiny
2019-03-29 1:00 ` Jerome Glisse
2019-03-29 1:18 ` John Hubbard
2019-03-29 1:50 ` Jerome Glisse
2019-03-28 18:21 ` Ira Weiny
2019-03-29 2:25 ` Jerome Glisse
2019-03-29 20:07 ` John Hubbard [this message]
2019-03-29 2:11 ` John Hubbard
2019-03-29 2:22 ` Jerome Glisse
2019-03-25 14:40 ` [PATCH v2 03/11] mm/hmm: do not erase snapshot when a range is invalidated jglisse
2019-03-25 14:40 ` [PATCH v2 04/11] mm/hmm: improve and rename hmm_vma_get_pfns() to hmm_range_snapshot() v2 jglisse
2019-03-28 13:30 ` Ira Weiny
2019-03-25 14:40 ` [PATCH v2 05/11] mm/hmm: improve and rename hmm_vma_fault() to hmm_range_fault() v2 jglisse
2019-03-28 13:43 ` Ira Weiny
2019-03-28 22:03 ` Jerome Glisse
2019-03-25 14:40 ` [PATCH v2 06/11] mm/hmm: improve driver API to work and wait over a range v2 jglisse
2019-03-28 13:11 ` Ira Weiny
2019-03-28 21:39 ` Jerome Glisse
2019-03-28 16:12 ` Ira Weiny
2019-03-29 0:56 ` Jerome Glisse
2019-03-28 18:49 ` Ira Weiny
2019-03-25 14:40 ` [PATCH v2 07/11] mm/hmm: add default fault flags to avoid the need to pre-fill pfns arrays jglisse
2019-03-28 21:59 ` John Hubbard
2019-03-28 22:12 ` Jerome Glisse
2019-03-28 22:19 ` John Hubbard
2019-03-28 22:31 ` Jerome Glisse
2019-03-28 22:40 ` John Hubbard
2019-03-28 23:21 ` Jerome Glisse
2019-03-28 23:28 ` John Hubbard
2019-03-28 16:42 ` Ira Weiny
2019-03-29 1:17 ` Jerome Glisse
2019-03-29 1:30 ` John Hubbard
2019-03-29 1:42 ` Jerome Glisse
2019-03-29 1:59 ` Jerome Glisse
2019-03-29 2:05 ` John Hubbard
2019-03-29 2:12 ` Jerome Glisse
2019-03-28 23:43 ` Jerome Glisse
2019-03-25 14:40 ` [PATCH v2 08/11] mm/hmm: mirror hugetlbfs (snapshoting, faulting and DMA mapping) v2 jglisse
2019-03-28 16:53 ` Ira Weiny
2019-03-25 14:40 ` [PATCH v2 09/11] mm/hmm: allow to mirror vma of a file on a DAX backed filesystem v2 jglisse
2019-03-28 18:04 ` Ira Weiny
2019-03-29 2:17 ` Jerome Glisse
2019-03-25 14:40 ` [PATCH v2 10/11] mm/hmm: add helpers for driver to safely take the mmap_sem v2 jglisse
2019-03-28 20:54 ` John Hubbard
2019-03-28 21:30 ` Jerome Glisse
2019-03-28 21:41 ` John Hubbard
2019-03-28 22:08 ` Jerome Glisse
2019-03-28 22:25 ` John Hubbard
2019-03-28 22:40 ` Jerome Glisse
2019-03-28 22:43 ` John Hubbard
2019-03-28 23:05 ` Jerome Glisse
2019-03-28 23:20 ` John Hubbard
2019-03-28 23:24 ` Jerome Glisse
2019-03-28 23:34 ` John Hubbard
2019-03-28 18:44 ` Ira Weiny
2019-03-25 14:40 ` [PATCH v2 11/11] mm/hmm: add an helper function that fault pages and map them to a device v2 jglisse
2019-04-01 11:59 ` Souptick Joarder
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