Re: [PATCH v3 09/10] drm/panfrost: Introduce huge tmpfs mount point option

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

On Sat,  4 Oct 2025 11:30:52 +0200
Loïc Molinari <loic.molinari@collabora.com> wrote:

> Introduce the 'panfrost.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).
> 
> v3:
> - use huge tmpfs mountpoint in drm_device
> 
> Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

A couple minor nits below.

> ---
>  drivers/gpu/drm/panfrost/panfrost_device.c |  3 +++
>  drivers/gpu/drm/panfrost/panfrost_drv.c    |  6 ++++++
>  drivers/gpu/drm/panfrost/panfrost_drv.h    | 11 +++++++++++
>  drivers/gpu/drm/panfrost/panfrost_gem.c    | 19 +++++++++++++++++++
>  drivers/gpu/drm/panfrost/panfrost_gem.h    |  2 ++
>  5 files changed, 41 insertions(+)
>  create mode 100644 drivers/gpu/drm/panfrost/panfrost_drv.h
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> index 04bec27449cb..a189bfaac959 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> @@ -12,6 +12,7 @@
>  #include "panfrost_device.h"
>  #include "panfrost_devfreq.h"
>  #include "panfrost_features.h"
> +#include "panfrost_gem.h"
>  #include "panfrost_issues.h"
>  #include "panfrost_gpu.h"
>  #include "panfrost_job.h"
> @@ -266,6 +267,8 @@ int panfrost_device_init(struct panfrost_device *pfdev)
>  	if (err)
>  		goto out_job;
>  
> +	panfrost_gem_init(pfdev);
> +
>  	return 0;
>  out_job:
>  	panfrost_job_fini(pfdev);
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index 22350ce8a08f..e376e70a3379 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -862,6 +862,12 @@ static const struct drm_driver panfrost_drm_driver = {
>  #endif
>  };
>  
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +bool panfrost_transparent_hugepage;
> +module_param_named(transparent_hugepage, panfrost_transparent_hugepage, bool, 0400);
> +MODULE_PARM_DESC(transparent_hugepage, "Use a dedicated tmpfs mount point with Transparent Hugepage enabled (false = default)");

Same here, I'd go for [panfrost_]enable_thp.

> +#endif
> +
>  static int panfrost_probe(struct platform_device *pdev)
>  {
>  	struct panfrost_device *pfdev;
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.h b/drivers/gpu/drm/panfrost/panfrost_drv.h
> new file mode 100644
> index 000000000000..60454611b6a6
> --- /dev/null
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.h
> @@ -0,0 +1,11 @@
> +// SPDX-License-Identifier: GPL-2.0 or MIT
> +/* Copyright 2025 Amazon.com, Inc. or its affiliates */
> +
> +#ifndef __PANFROST_DRV_H__
> +#define __PANFROST_DRV_H__
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +extern bool panfrost_transparent_hugepage;
> +#endif
> +
> +#endif
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index 85d6289a6eda..c3883a639e13 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -1,5 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  /* Copyright 2019 Linaro, Ltd, Rob Herring <robh@kernel.org> */
> +/* Copyright 2025 Amazon.com, Inc. or its affiliates */
>  
>  #include <linux/cleanup.h>
>  #include <linux/err.h>
> @@ -9,9 +10,27 @@
>  
>  #include <drm/panfrost_drm.h>
>  #include "panfrost_device.h"
> +#include "panfrost_drv.h"
>  #include "panfrost_gem.h"
>  #include "panfrost_mmu.h"
>  
> +void panfrost_gem_init(struct panfrost_device *pfdev)
> +{
> +	int err;
> +
> +	if (!panfrost_transparent_hugepage)
> +		return;
> +
> +	err = drm_gem_huge_mnt_create(pfdev->ddev, "within_size");
> +	if (err && err != -EEXIST) {
> +		drm_warn(pfdev->ddev, "Can't use Transparent Hugepage (%d)\n",
> +			 -err);

I think errors are printed as negative values elsewhere, so I'd stick to err
not -err here.

> +		return;
> +	}
> +
> +	drm_info(pfdev->ddev, "Using Transparent Hugepage\n");


Here's a shorter version of the same thing (I dropped the EEXIST based on
my comment on patch 3).

	if (err)
		drm_warn(pfdev->ddev, "Can't use Transparent Hugepage (err=%d)\n", err);
	else
		drm_info(pfdev->ddev, "Using Transparent Hugepage\n");

> +}
> +
>  #ifdef CONFIG_DEBUG_FS
>  static void panfrost_gem_debugfs_bo_add(struct panfrost_device *pfdev,
>  					struct panfrost_gem_object *bo)
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
> index 8de3e76f2717..1a62529ff06f 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
> @@ -124,6 +124,8 @@ drm_mm_node_to_panfrost_mapping(struct drm_mm_node *node)
>  	return container_of(node, struct panfrost_gem_mapping, mmnode);
>  }
>  
> +void panfrost_gem_init(struct panfrost_device *pfdev);
> +
>  struct drm_gem_object *panfrost_gem_create_object(struct drm_device *dev, size_t size);
>  
>  struct drm_gem_object *