Re: [PATCH v3 6/6] drm/gem-shmem: Track folio accessed/dirty status in vmap

[Thomas Zimmermann <tzimmermann@suse.de>]

Am 25.02.26 um 11:57 schrieb Frank Binns:
> Hi Thomas,
>
> On Mon, 2026-02-09 at 14:27 +0100, Thomas Zimmermann wrote:
>> On successful vmap, set the page_mark_accessed_on_put and _dirty_on_put
>> flags in the gem-shmem object. Signals that the contained pages require
>> LRU and dirty tracking when they are being released back to SHMEM. Clear
>> these flags on put, so that the buffer remains quiet until the next call
>> to vmap. There's no means of handling dirty status in vmap as there's no
>> write-only mapping available.
>>
>> Both flags, _accessed_on_put and _dirty_on_put, have always been part of
>> the gem-shmem object, but never used much. So most drivers did not track
>> the page status correctly.
>>
>> Only the v3d and imagination drivers make limited use of _dirty_on_put. In
>> the case of imagination, move the flag setting from init to cleanup. This
>> ensures writeback of modified pages but does not interfere with the
>> internal vmap/vunmap calls. V3d already implements this behaviour.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com> # gem-shmem
> The change to the imagination driver is:
>
> Acked-by: Frank Binns <frank.binns@imgtec.com>
> Tested-by: Frank Binns <frank.binns@imgtec.com>

Great, thanks a lot.

>
> Thanks
> Frank
>
>> ---
>>   drivers/gpu/drm/drm_gem_shmem_helper.c | 4 ++++
>>   drivers/gpu/drm/imagination/pvr_gem.c  | 6 ++++--
>>   2 files changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
>> index 0c86ad40a049..dda9af9bf5b3 100644
>> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
>> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
>> @@ -265,6 +265,8 @@ void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
>>   				  shmem->pages_mark_dirty_on_put,
>>   				  shmem->pages_mark_accessed_on_put);
>>   		shmem->pages = NULL;
>> +		shmem->pages_mark_accessed_on_put = false;
>> +		shmem->pages_mark_dirty_on_put = false;
>>   	}
>>   }
>>   EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked);
>> @@ -397,6 +399,8 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
>>   		} else {
>>   			iosys_map_set_vaddr(map, shmem->vaddr);
>>   			refcount_set(&shmem->vmap_use_count, 1);
>> +			shmem->pages_mark_accessed_on_put = true;
>> +			shmem->pages_mark_dirty_on_put = true;
>>   		}
>>   	}
>>   
>> diff --git a/drivers/gpu/drm/imagination/pvr_gem.c b/drivers/gpu/drm/imagination/pvr_gem.c
>> index c07c9a915190..307b02c916d4 100644
>> --- a/drivers/gpu/drm/imagination/pvr_gem.c
>> +++ b/drivers/gpu/drm/imagination/pvr_gem.c
>> @@ -25,7 +25,10 @@
>>   
>>   static void pvr_gem_object_free(struct drm_gem_object *obj)
>>   {
>> -	drm_gem_shmem_object_free(obj);
>> +	struct drm_gem_shmem_object *shmem_obj = to_drm_gem_shmem_obj(obj);
>> +
>> +	shmem_obj->pages_mark_dirty_on_put = true;
>> +	drm_gem_shmem_free(shmem_obj);
>>   }
>>   
>>   static struct dma_buf *pvr_gem_export(struct drm_gem_object *obj, int flags)
>> @@ -363,7 +366,6 @@ pvr_gem_object_create(struct pvr_device *pvr_dev, size_t size, u64 flags)
>>   	if (IS_ERR(shmem_obj))
>>   		return ERR_CAST(shmem_obj);
>>   
>> -	shmem_obj->pages_mark_dirty_on_put = true;
>>   	shmem_obj->map_wc = !(flags & PVR_BO_CPU_CACHED);
>>   	pvr_obj = shmem_gem_to_pvr_gem(shmem_obj);
>>   	pvr_obj->flags = flags;

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)