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[PATCH v13 03/10] drm/shmem-helper: Add pages_pin_count field

Dmitry Osipenko posted 10 patches 2 years, 11 months ago
There is a newer version of this series
[PATCH v13 03/10] drm/shmem-helper: Add pages_pin_count field
Posted by Dmitry Osipenko 2 years, 11 months ago 
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@collabora.com>
---
 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;
+
 	/**
 	 * @madv: State for madvise
 	 *
-- 
2.39.2
Re: [PATCH v13 03/10] drm/shmem-helper: Add pages_pin_count field
Posted by Boris Brezillon 2 years, 7 months ago 
Hi Dmitry,

Sorry for chiming in only now :-/.

On Tue, 14 Mar 2023 05:26:52 +0300
Dmitry Osipenko <dmitry.osipenko@collabora.com> 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@collabora.com>
> ---
>  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.

Regards,

Boris
Re: [PATCH v13 03/10] drm/shmem-helper: Add pages_pin_count field
Posted by Boris Brezillon 2 years, 7 months ago 
On Mon, 26 Jun 2023 17:04:57 +0200
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> Hi Dmitry,
> 
> Sorry for chiming in only now :-/.
> 
> On Tue, 14 Mar 2023 05:26:52 +0300
> Dmitry Osipenko <dmitry.osipenko@collabora.com> 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@collabora.com>
> > ---
> >  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.
Re: [PATCH v13 03/10] drm/shmem-helper: Add pages_pin_count field
Posted by Dmitry Osipenko 2 years, 7 months ago 
On 6/26/23 18:21, Boris Brezillon wrote:
> On Mon, 26 Jun 2023 17:04:57 +0200
> Boris Brezillon <boris.brezillon@collabora.com> wrote:
> 
>> Hi Dmitry,
>>
>> Sorry for chiming in only now :-/.
>>
>> On Tue, 14 Mar 2023 05:26:52 +0300
>> Dmitry Osipenko <dmitry.osipenko@collabora.com> 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@collabora.com>
>>> ---
>>>  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

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