Re: [PATCH 6/8] drm/panthor: Introduce huge tmpfs mount point option

[Boris Brezillon <boris.brezillon@collabora.com>]

On Mon, 29 Sep 2025 22:03:14 +0200
Loïc Molinari <loic.molinari@collabora.com> wrote:

> Introduce the 'panthor.transparent_hugepage' boolean module parameter
> (false by default). When the parameter is set to true, a new tmpfs
> mount point is created and mounted using the 'huge=within_size'
> option. It's then used at GEM object creation instead of the default
> 'shm_mnt' mount point in order to enable Transparent Hugepage (THP)
> for the object (without having to rely on a system wide parameter).
> 
> Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_device.c |  4 ++++
>  drivers/gpu/drm/panthor/panthor_device.h |  3 +++
>  drivers/gpu/drm/panthor/panthor_drv.c    |  7 ++++++
>  drivers/gpu/drm/panthor/panthor_drv.h    | 11 +++++++++
>  drivers/gpu/drm/panthor/panthor_gem.c    | 30 +++++++++++++++++++++++-
>  drivers/gpu/drm/panthor/panthor_gem.h    |  3 +++
>  6 files changed, 57 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/gpu/drm/panthor/panthor_drv.h
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index 81df49880bd8..4f254b574287 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -17,6 +17,7 @@
>  #include "panthor_devfreq.h"
>  #include "panthor_device.h"
>  #include "panthor_fw.h"
> +#include "panthor_gem.h"
>  #include "panthor_gpu.h"
>  #include "panthor_hw.h"
>  #include "panthor_mmu.h"
> @@ -98,6 +99,7 @@ void panthor_device_unplug(struct panthor_device *ptdev)
>  	/* Now, try to cleanly shutdown the GPU before the device resources
>  	 * get reclaimed.
>  	 */
> +	panthor_gem_fini(ptdev);
>  	panthor_sched_unplug(ptdev);
>  	panthor_fw_unplug(ptdev);
>  	panthor_mmu_unplug(ptdev);
> @@ -269,6 +271,8 @@ int panthor_device_init(struct panthor_device *ptdev)
>  	if (ret)
>  		goto err_unplug_fw;
>  
> +	panthor_gem_init(ptdev);
> +
>  	/* ~3 frames */
>  	pm_runtime_set_autosuspend_delay(ptdev->base.dev, 50);
>  	pm_runtime_use_autosuspend(ptdev->base.dev);
> diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> index 4fc7cf2aeed5..54ca61567426 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.h
> +++ b/drivers/gpu/drm/panthor/panthor_device.h
> @@ -135,6 +135,9 @@ struct panthor_device {
>  	/** @devfreq: Device frequency scaling management data. */
>  	struct panthor_devfreq *devfreq;
>  
> +	/** @huge_mnt: tmpfs mount point with Transparent Hugepage enabled. */
> +	struct vfsmount *huge_mnt;

Now that we have a helper to create a huge mountpoint, wouldn't it
make sense to have this field in drm_device instead of having each
driver add a huge_mnt field to their <driver>_device object.

> +
>  	/** @unplug: Device unplug related fields. */
>  	struct {
>  		/** @lock: Lock used to serialize unplug operations. */
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index fdbe89ef7f43..a2be3b904ca2 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -1556,6 +1556,7 @@ static const struct file_operations panthor_drm_driver_fops = {
>  	.read = drm_read,
>  	.llseek = noop_llseek,
>  	.mmap = panthor_mmap,
> +	.get_unmapped_area = drm_gem_get_unmapped_area,
>  	.show_fdinfo = drm_show_fdinfo,
>  	.fop_flags = FOP_UNSIGNED_OFFSET,
>  };
> @@ -1623,6 +1624,12 @@ static const struct drm_driver panthor_drm_driver = {
>  #endif
>  };
>  
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +bool panthor_transparent_hugepage;
> +module_param_named(transparent_hugepage, panthor_transparent_hugepage, bool, 0400);
> +MODULE_PARM_DESC(transparent_hugepage, "Use a dedicated tmpfs mount point with Transparent Hugepage enabled (false = default)");
> +#endif
> +
>  static int panthor_probe(struct platform_device *pdev)
>  {
>  	struct panthor_device *ptdev;
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.h b/drivers/gpu/drm/panthor/panthor_drv.h
> new file mode 100644
> index 000000000000..27fe9b6f77bd
> --- /dev/null
> +++ b/drivers/gpu/drm/panthor/panthor_drv.h
> @@ -0,0 +1,11 @@
> +// SPDX-License-Identifier: GPL-2.0 or MIT
> +/* Copyright 2025 Amazon.com, Inc. or its affiliates */
> +
> +#ifndef __PANTHOR_DRV_H__
> +#define __PANTHOR_DRV_H__
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +extern bool panthor_transparent_hugepage;
> +#endif
> +
> +#endif
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index 156c7a0b62a2..16916e0b6d89 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -1,6 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0 or MIT
>  /* Copyright 2019 Linaro, Ltd, Rob Herring <robh@kernel.org> */
>  /* Copyright 2023 Collabora ltd. */
> +/* Copyright 2025 Amazon.com, Inc. or its affiliates */
>  
>  #include <linux/cleanup.h>
>  #include <linux/dma-buf.h>
> @@ -11,10 +12,35 @@
>  #include <drm/panthor_drm.h>
>  
>  #include "panthor_device.h"
> +#include "panthor_drv.h"
>  #include "panthor_fw.h"
>  #include "panthor_gem.h"
>  #include "panthor_mmu.h"
>  
> +void panthor_gem_init(struct panthor_device *ptdev)
> +{
> +	struct vfsmount *huge_mnt;
> +
> +	if (!panthor_transparent_hugepage)
> +		return;
> +
> +	huge_mnt = drm_gem_shmem_huge_mnt_create("within_size");
> +	if (IS_ERR(huge_mnt)) {
> +		drm_warn(&ptdev->base, "Can't use Transparent Hugepage (%ld)\n",
> +			 PTR_ERR(huge_mnt));
> +		return;
> +	}
> +
> +	ptdev->huge_mnt = huge_mnt;
> +
> +	drm_info(&ptdev->base, "Using Transparent Hugepage\n");
> +}
> +
> +void panthor_gem_fini(struct panthor_device *ptdev)
> +{
> +	drm_gem_shmem_huge_mnt_free(ptdev->huge_mnt);
> +}
> +
>  #ifdef CONFIG_DEBUG_FS
>  static void panthor_gem_debugfs_bo_init(struct panthor_gem_object *bo)
>  {
> @@ -270,10 +296,12 @@ panthor_gem_create_with_handle(struct drm_file *file,
>  			       u64 *size, u32 flags, u32 *handle)
>  {
>  	int ret;
> +	struct panthor_device *ptdev =
> +		container_of(ddev, struct panthor_device, base);
>  	struct drm_gem_shmem_object *shmem;
>  	struct panthor_gem_object *bo;
>  
> -	shmem = drm_gem_shmem_create(ddev, *size);
> +	shmem = drm_gem_shmem_create_with_mnt(ddev, *size, ptdev->huge_mnt);
>  	if (IS_ERR(shmem))
>  		return PTR_ERR(shmem);
>  
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
> index 80c6e24112d0..6804b3912cc2 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.h
> +++ b/drivers/gpu/drm/panthor/panthor_gem.h
> @@ -136,6 +136,9 @@ struct panthor_gem_object *to_panthor_bo(struct drm_gem_object *obj)
>  	return container_of(to_drm_gem_shmem_obj(obj), struct panthor_gem_object, base);
>  }
>  
> +void panthor_gem_init(struct panthor_device *ptdev);
> +void panthor_gem_fini(struct panthor_device *ptdev);
> +
>  struct drm_gem_object *panthor_gem_create_object(struct drm_device *ddev, size_t size);
>  
>  int