Re: [PATCH v4 07/13] drm/v3d: Use huge tmpfs mount point helper

[Tvrtko Ursulin <tursulin@ursulin.net>]

On 15/10/2025 16:30, Loïc Molinari wrote:
> Make use of the new drm_gem_huge_mnt_create() helper to avoid code
> duplication. Now that it's just a few lines long, the single function
> in v3d_gemfs.c is moved into v3d_gem.c.
> 
> v3:
> - use huge tmpfs mountpoint in drm_device
> - move v3d_gemfs.c into v3d_gem.c
> 
> v4:
> - clean up mountpoint creation error handling
> 
> Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
> ---
>   drivers/gpu/drm/v3d/Makefile    |  3 +-
>   drivers/gpu/drm/v3d/v3d_bo.c    |  5 ++-
>   drivers/gpu/drm/v3d/v3d_drv.c   |  2 +-
>   drivers/gpu/drm/v3d/v3d_drv.h   | 11 +-----
>   drivers/gpu/drm/v3d/v3d_gem.c   | 27 +++++++++++++--
>   drivers/gpu/drm/v3d/v3d_gemfs.c | 60 ---------------------------------
>   6 files changed, 30 insertions(+), 78 deletions(-)
>   delete mode 100644 drivers/gpu/drm/v3d/v3d_gemfs.c
> 
> diff --git a/drivers/gpu/drm/v3d/Makefile b/drivers/gpu/drm/v3d/Makefile
> index fcf710926057..b7d673f1153b 100644
> --- a/drivers/gpu/drm/v3d/Makefile
> +++ b/drivers/gpu/drm/v3d/Makefile
> @@ -13,8 +13,7 @@ v3d-y := \
>   	v3d_trace_points.o \
>   	v3d_sched.o \
>   	v3d_sysfs.o \
> -	v3d_submit.o \
> -	v3d_gemfs.o
> +	v3d_submit.o
>   
>   v3d-$(CONFIG_DEBUG_FS) += v3d_debugfs.o
>   
> diff --git a/drivers/gpu/drm/v3d/v3d_bo.c b/drivers/gpu/drm/v3d/v3d_bo.c
> index c41476ddde68..6b9909bfce82 100644
> --- a/drivers/gpu/drm/v3d/v3d_bo.c
> +++ b/drivers/gpu/drm/v3d/v3d_bo.c
> @@ -112,7 +112,7 @@ v3d_bo_create_finish(struct drm_gem_object *obj)
>   	if (IS_ERR(sgt))
>   		return PTR_ERR(sgt);
>   
> -	if (!v3d->gemfs)
> +	if (!obj->dev->huge_mnt)

Maybe it would be a good idea to add a helper for this check. Keeping 
aligned with drm_gem_huge_mnt_create() something like 
drm_gem_has_huge_mnt()? That would then hide the optional drm_device 
struct member if you decide to go for that.

>   		align = SZ_4K;
>   	else if (obj->size >= SZ_1M)
>   		align = SZ_1M;
> @@ -148,12 +148,11 @@ struct v3d_bo *v3d_bo_create(struct drm_device *dev, struct drm_file *file_priv,
>   			     size_t unaligned_size)
>   {
>   	struct drm_gem_shmem_object *shmem_obj;
> -	struct v3d_dev *v3d = to_v3d_dev(dev);
>   	struct v3d_bo *bo;
>   	int ret;
>   
>   	shmem_obj = drm_gem_shmem_create_with_mnt(dev, unaligned_size,
> -						  v3d->gemfs);
> +						  dev->huge_mnt);

Okay this one goes away by the end of the series.

>   	if (IS_ERR(shmem_obj))
>   		return ERR_CAST(shmem_obj);
>   	bo = to_v3d_bo(&shmem_obj->base);
> diff --git a/drivers/gpu/drm/v3d/v3d_drv.c b/drivers/gpu/drm/v3d/v3d_drv.c
> index c5a3bbbc74c5..19ec0ea7f38e 100644
> --- a/drivers/gpu/drm/v3d/v3d_drv.c
> +++ b/drivers/gpu/drm/v3d/v3d_drv.c
> @@ -106,7 +106,7 @@ static int v3d_get_param_ioctl(struct drm_device *dev, void *data,
>   		args->value = v3d->perfmon_info.max_counters;
>   		return 0;
>   	case DRM_V3D_PARAM_SUPPORTS_SUPER_PAGES:
> -		args->value = !!v3d->gemfs;
> +		args->value = !!dev->huge_mnt;
>   		return 0;
>   	case DRM_V3D_PARAM_GLOBAL_RESET_COUNTER:
>   		mutex_lock(&v3d->reset_lock);
> diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h
> index 1884686985b8..99a39329bb85 100644
> --- a/drivers/gpu/drm/v3d/v3d_drv.h
> +++ b/drivers/gpu/drm/v3d/v3d_drv.h
> @@ -158,11 +158,6 @@ struct v3d_dev {
>   	struct drm_mm mm;
>   	spinlock_t mm_lock;
>   
> -	/*
> -	 * tmpfs instance used for shmem backed objects
> -	 */
> -	struct vfsmount *gemfs;
> -
>   	struct work_struct overflow_mem_work;
>   
>   	struct v3d_queue_state queue[V3D_MAX_QUEUES];
> @@ -569,6 +564,7 @@ extern const struct dma_fence_ops v3d_fence_ops;
>   struct dma_fence *v3d_fence_create(struct v3d_dev *v3d, enum v3d_queue q);
>   
>   /* v3d_gem.c */
> +extern bool super_pages;
>   int v3d_gem_init(struct drm_device *dev);
>   void v3d_gem_destroy(struct drm_device *dev);
>   void v3d_reset_sms(struct v3d_dev *v3d);
> @@ -576,11 +572,6 @@ void v3d_reset(struct v3d_dev *v3d);
>   void v3d_invalidate_caches(struct v3d_dev *v3d);
>   void v3d_clean_caches(struct v3d_dev *v3d);
>   
> -/* v3d_gemfs.c */
> -extern bool super_pages;
> -void v3d_gemfs_init(struct v3d_dev *v3d);
> -void v3d_gemfs_fini(struct v3d_dev *v3d);
> -
>   /* v3d_submit.c */
>   void v3d_job_cleanup(struct v3d_job *job);
>   void v3d_job_put(struct v3d_job *job);
> diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
> index bb110d35f749..635ff0fabe7e 100644
> --- a/drivers/gpu/drm/v3d/v3d_gem.c
> +++ b/drivers/gpu/drm/v3d/v3d_gem.c
> @@ -258,6 +258,30 @@ v3d_invalidate_caches(struct v3d_dev *v3d)
>   	v3d_invalidate_slices(v3d, 0);
>   }
>   
> +static void
> +v3d_huge_mnt_init(struct v3d_dev *v3d)
> +{
> +	int err = 0;
> +
> +	/*
> +	 * By using a huge shmemfs mountpoint when the user wants to
> +	 * enable Super Pages, we can pass in mount flags that better
> +	 * match our usecase.
> +	 */
> +
> +	if (super_pages)
> +		err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");

If it is this patch that is creating the build failure then the two 
should be squashed.

Then in "drm/v3d: Fix builds with CONFIG_TRANSPARENT_HUGEPAGE=n" this 
ends up a bit ugly:

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
  	if (super_pages)
#endif
  		err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");

Does this not work:

  	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && super_pages)
  		err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");

?

Regards,

Tvrtko

> +
> +	if (v3d->drm.huge_mnt)
> +		drm_info(&v3d->drm, "Using Transparent Hugepages\n");
> +	else if (err)
> +		drm_warn(&v3d->drm, "Can't use Transparent Hugepages (%d)\n",
> +			 err);
> +	else
> +		drm_notice(&v3d->drm,
> +			   "Transparent Hugepage support is recommended for optimal performance on this platform!\n");
> +}
> +
>   int
>   v3d_gem_init(struct drm_device *dev)
>   {
> @@ -309,7 +333,7 @@ v3d_gem_init(struct drm_device *dev)
>   	v3d_init_hw_state(v3d);
>   	v3d_mmu_set_page_table(v3d);
>   
> -	v3d_gemfs_init(v3d);
> +	v3d_huge_mnt_init(v3d);
>   
>   	ret = v3d_sched_init(v3d);
>   	if (ret) {
> @@ -329,7 +353,6 @@ v3d_gem_destroy(struct drm_device *dev)
>   	enum v3d_queue q;
>   
>   	v3d_sched_fini(v3d);
> -	v3d_gemfs_fini(v3d);
>   
>   	/* Waiting for jobs to finish would need to be done before
>   	 * unregistering V3D.
> diff --git a/drivers/gpu/drm/v3d/v3d_gemfs.c b/drivers/gpu/drm/v3d/v3d_gemfs.c
> deleted file mode 100644
> index c1a30166c099..000000000000
> --- a/drivers/gpu/drm/v3d/v3d_gemfs.c
> +++ /dev/null
> @@ -1,60 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0+
> -/* Copyright (C) 2024 Raspberry Pi */
> -
> -#include <linux/fs.h>
> -#include <linux/mount.h>
> -#include <linux/fs_context.h>
> -
> -#include "v3d_drv.h"
> -
> -void v3d_gemfs_init(struct v3d_dev *v3d)
> -{
> -	struct file_system_type *type;
> -	struct fs_context *fc;
> -	struct vfsmount *gemfs;
> -	int ret;
> -
> -	/*
> -	 * By creating our own shmemfs mountpoint, we can pass in
> -	 * mount flags that better match our usecase. However, we
> -	 * only do so on platforms which benefit from it.
> -	 */
> -	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> -		goto err;
> -
> -	/* The user doesn't want to enable Super Pages */
> -	if (!super_pages)
> -		goto err;
> -
> -	type = get_fs_type("tmpfs");
> -	if (!type)
> -		goto err;
> -
> -	fc = fs_context_for_mount(type, SB_KERNMOUNT);
> -	if (IS_ERR(fc))
> -		goto err;
> -	ret = vfs_parse_fs_string(fc, "source", "tmpfs");
> -	if (!ret)
> -		ret = vfs_parse_fs_string(fc, "huge", "within_size");
> -	if (!ret)
> -		gemfs = fc_mount_longterm(fc);
> -	put_fs_context(fc);
> -	if (ret)
> -		goto err;
> -
> -	v3d->gemfs = gemfs;
> -	drm_info(&v3d->drm, "Using Transparent Hugepages\n");
> -
> -	return;
> -
> -err:
> -	v3d->gemfs = NULL;
> -	drm_notice(&v3d->drm,
> -		   "Transparent Hugepage support is recommended for optimal performance on this platform!\n");
> -}
> -
> -void v3d_gemfs_fini(struct v3d_dev *v3d)
> -{
> -	if (v3d->gemfs)
> -		kern_unmount(v3d->gemfs);
> -}