On 6/26/23 18:21, Boris Brezillon wrote:
> On Mon, 26 Jun 2023 17:04:57 +0200
> Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> wrote:
>
>> Hi Dmitry,
>>
>> Sorry for chiming in only now :-/.
>>
>> On Tue, 14 Mar 2023 05:26:52 +0300
>> Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> wrote:
>>
>>> And new pages_pin_count field to struct drm_gem_shmem_object that will
>>> determine whether pages are evictable by memory shrinker. The pages will
>>> be evictable only when pages_pin_count=0. This patch prepares code for
>>> addition of the memory shrinker that will utilize the new field.
>>>
>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
>>> ---
>>> drivers/gpu/drm/drm_gem_shmem_helper.c | 7 +++++++
>>> include/drm/drm_gem_shmem_helper.h | 9 +++++++++
>>> 2 files changed, 16 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
>>> index 4da9c9c39b9a..81d61791f874 100644
>>> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
>>> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
>>> @@ -277,6 +277,8 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
>>> drm_WARN_ON(obj->dev, obj->import_attach);
>>>
>>> ret = drm_gem_shmem_get_pages(shmem);
>>> + if (!ret)
>>> + shmem->pages_pin_count++;
>>>
>>> return ret;
>>> }
>>> @@ -289,7 +291,12 @@ static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
>>>
>>> drm_WARN_ON(obj->dev, obj->import_attach);
>>>
>>> + if (drm_WARN_ON_ONCE(obj->dev, !shmem->pages_pin_count))
>>> + return;
>>> +
>>> drm_gem_shmem_put_pages(shmem);
>>> +
>>> + shmem->pages_pin_count--;
>>> }
>>>
>>> /**
>>> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
>>> index 20ddcd799df9..7d823c9fc480 100644
>>> --- a/include/drm/drm_gem_shmem_helper.h
>>> +++ b/include/drm/drm_gem_shmem_helper.h
>>> @@ -39,6 +39,15 @@ struct drm_gem_shmem_object {
>>> */
>>> unsigned int pages_use_count;
>>>
>>> + /**
>>> + * @pages_pin_count:
>>> + *
>>> + * Reference count on the pinned pages table.
>>> + * The pages allowed to be evicted by memory shrinker
>>> + * only when the count is zero.
>>> + */
>>> + unsigned int pages_pin_count;
>>
>> s/pages_pin_count/pin_count/ ?
>>
>> And do we really need both pages_pin_count and pages_use_count. Looks
>> like they both serve the same purpose, with one exception:
>> pages_use_count is also incremented in the get_pages_sgt_locked() path,
>> but you probably don't want it to prevent GEM eviction. Assuming
>> your goal with this pin_count field is to check if a GEM object is
>> evictable, it can be done with something like
>>
>> bool
>> drm_gem_shmem_is_evictable_locked(struct drm_gem_shmem_object *shmem)
>> {
>> dma_resv_assert_held(shmem->base.resv);
>>
>> return shmem->pages_use_count == (shmem->sgt ? 1 : 0);
>> }
>>
>> I mean, I'm not against renaming pages_use_count into pin_count, but,
>> unless I'm missing something, I don't see a good reason to keep both.
>
> My bad, I think I found one place calling drm_gem_shmem_get_pages()
> where we want pin_count and pages_use_count to differ:
> drm_gem_shmem_mmap(). We certainly don't want userspace mappings to
> prevent eviction.
That's correct, thanks for the review :)
--
Best regards,
Dmitry
