Re: [PATCH v10 08/10] drm/panthor: Introduce huge tmpfs mountpoint option

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

On Fri, 28 Nov 2025 19:52:50 +0100
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
> mountpoint is created and mounted using the 'huge=within_size'
> option. It's then used at GEM object creation instead of the default
> 'shm_mnt' mountpoint 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
> 
> v4:
> - fix builds with CONFIG_TRANSPARENT_HUGEPAGE=n
> - clean up mountpoint creation error handling
> - print negative error value
> 
> v5:
> - use drm_gem_has_huge_tmp() helper
> - get rid of CONFIG_TRANSPARENT_HUGEPAGE ifdefs
> 
> v9:
> - replace drm_gem_has_huge_tmp() by drm_gem_get_huge_tmp()
> 
> Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_device.c |  3 +++
>  drivers/gpu/drm/panthor/panthor_drv.c    |  7 +++++++
>  drivers/gpu/drm/panthor/panthor_drv.h    |  9 +++++++++
>  drivers/gpu/drm/panthor/panthor_gem.c    | 18 ++++++++++++++++++
>  drivers/gpu/drm/panthor/panthor_gem.h    |  2 ++
>  5 files changed, 39 insertions(+)
>  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 e133b1e0ad6d..2979ee0e52c2 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -18,6 +18,7 @@
>  #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"
> @@ -294,6 +295,8 @@ 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_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index d1d4c50da5bf..55dbda6dbf9c 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -1559,6 +1559,7 @@ 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,
>  };
> @@ -1626,6 +1627,12 @@ 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)");

On a second thought, I wonder if this shouldn't be an opt-out param
(which is what V3D does, BTW). What's the downside of enabling THP if we
have a fallback for cases where memory is too fragmented to get huge
pages at allocation time?

> +#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..79dccd289881
> --- /dev/null
> +++ b/drivers/gpu/drm/panthor/panthor_drv.h
> @@ -0,0 +1,9 @@
> +// SPDX-License-Identifier: GPL-2.0 or MIT
> +/* Copyright 2025 Amazon.com, Inc. or its affiliates */
> +
> +#ifndef __PANTHOR_DRV_H__
> +#define __PANTHOR_DRV_H__
> +
> +extern bool panthor_transparent_hugepage;
> +
> +#endif
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index 10d255cccc09..7ae07a9bc996 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>
> @@ -12,10 +13,27 @@
>  #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)
> +{
> +	int err;
> +
> +	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
> +	    !panthor_transparent_hugepage)
> +		return;
> +
> +	err = drm_gem_huge_mnt_create(&ptdev->base, "within_size");
> +	if (drm_gem_get_huge_mnt(&ptdev->base))
> +		drm_info(&ptdev->base, "Using Transparent Hugepage\n");
> +	else if (err)
> +		drm_warn(&ptdev->base, "Can't use Transparent Hugepage (%d)\n",
> +			 err);
> +}
> +
>  #ifdef CONFIG_DEBUG_FS
>  static void panthor_gem_debugfs_bo_init(struct panthor_gem_object *bo)
>  {
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
> index 80c6e24112d0..2eefe9104e5e 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.h
> +++ b/drivers/gpu/drm/panthor/panthor_gem.h
> @@ -136,6 +136,8 @@ 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);
> +
>  struct drm_gem_object *panthor_gem_create_object(struct drm_device *ddev, size_t size);
>  
>  int