[PATCH v13 04/10] drm/gem: Add huge tmpfs mountpoint helpers

Loïc Molinari
2025-12-05T18:22:49Z

Add the drm_gem_huge_mnt_create() and drm_gem_get_huge_mnt() helpers
to avoid code duplication in the i915, V3D, Panfrost and Panthor
drivers. The former creates and mounts a dedicated huge tmpfs
mountpoint, for the lifetime of a DRM device, used at GEM object
initialization. The latter retrieves the dedicated huge tmpfs
mountpoint used by a DRM device.

The next commits will port drivers to these helpers.

v3:
- store huge tmpfs mountpoint in drm_device

v4:
- return 0 in builds with CONFIG_TRANSPARENT_HUGEPAGE=n
- return 0 when huge_mnt already exists
- use new vfs_parse_fs_string() helper

v5:
- remove warning on !dev->huge_mnt and reset to NULL on free
- inline drm_gem_huge_mnt_create() to remove func from text and avoid
calls in builds with CONFIG_TRANSPARENT_HUGEPAGE=n
- compile out drm_device's huge_mnt field in builds with
CONFIG_TRANSPARENT_HUGEPAGE=n
- add drm_gem_has_huge_mnt() helper

v6:
- move huge_mnt doc into ifdef'd section
- either inline or export drm_gem_huge_mnt_create()

v7:
- include <drm/drm_device.h> in drm_gem.h

v9:
- replace drm_gem_has_huge_mnt() by drm_gem_get_huge_mnt()

v11:
- doc fixes
- add Boris and Maíra R-bs

Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
---
drivers/gpu/drm/drm_gem.c | 57 +++++++++++++++++++++++++++++++++++++++
include/drm/drm_device.h | 15 +++++++++++
include/drm/drm_gem.h | 33 +++++++++++++++++++++++
3 files changed, 105 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 933fc89dd648..32dddb23e211 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -29,6 +29,9 @@
#include <linux/export.h>
#include <linux/file.h>
#include <linux/fs.h>
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#include <linux/fs_context.h>
+#endif
#include <linux/iosys-map.h>
#include <linux/mem_encrypt.h>
#include <linux/mm.h>
@@ -82,6 +85,60 @@
* up at a later date, and as our interface with shmfs for memory allocation.
*/

+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static void drm_gem_huge_mnt_free(struct drm_device *dev, void *data)
+{
+ kern_unmount(dev->huge_mnt);
+}
+
+/**
+ * drm_gem_huge_mnt_create - Create, mount and use a huge tmpfs mountpoint
+ * @dev: DRM device that will use the huge tmpfs mountpoint
+ * @value: huge tmpfs mount option value
+ *
+ * This function creates and mounts a dedicated huge tmpfs mountpoint for the
+ * lifetime of the DRM device @dev which is used at GEM object initialization
+ * with drm_gem_object_init().
+ *
+ * The most common option for @value is "within_size" which only allocates huge
+ * pages if the page will be fully within the GEM object size. "always",
+ * "advise" and "never" are supported too but the latter would just create a
+ * mountpoint similar to the default one (`shm_mnt`). See shmemfs and
+ * Transparent Hugepage for more information.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
+ */
+int drm_gem_huge_mnt_create(struct drm_device *dev, const char *value)
+{
+ struct file_system_type *type;
+ struct fs_context *fc;
+ int ret;
+
+ if (unlikely(drm_gem_get_huge_mnt(dev)))
+ return 0;
+
+ type = get_fs_type("tmpfs");
+ if (unlikely(!type))
+ return -EOPNOTSUPP;
+ fc = fs_context_for_mount(type, SB_KERNMOUNT);
+ if (IS_ERR(fc))
+ return PTR_ERR(fc);
+ ret = vfs_parse_fs_string(fc, "source", "tmpfs");
+ if (unlikely(ret))
+ return -ENOPARAM;
+ ret = vfs_parse_fs_string(fc, "huge", value);
+ if (unlikely(ret))
+ return -ENOPARAM;
+
+ dev->huge_mnt = fc_mount_longterm(fc);
+ put_fs_context(fc);
+
+ return drmm_add_action_or_reset(dev, drm_gem_huge_mnt_free, NULL);
+}
+EXPORT_SYMBOL_GPL(drm_gem_huge_mnt_create);
+#endif
+
static void
drm_gem_init_release(struct drm_device *dev, void *ptr)
{
diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
index 5af49c5c3778..bc78fb77cc27 100644
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -3,6 +3,9 @@

#include <linux/list.h>
#include <linux/kref.h>
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#include <linux/mount.h>
+#endif
#include <linux/mutex.h>
#include <linux/idr.h>
#include <linux/sched.h>
@@ -168,6 +171,18 @@ struct drm_device {
*/
struct drm_master *master;

+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ /**
+ * @huge_mnt:
+ *
+ * Huge tmpfs mountpoint used at GEM object initialization
+ * drm_gem_object_init(). Drivers can call drm_gem_huge_mnt_create() to
+ * create, mount and use it. The default tmpfs mountpoint (`shm_mnt`) is
+ * used if NULL.
+ */
+ struct vfsmount *huge_mnt;
+#endif
+
/**
* @driver_features: per-device driver features
*
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 7c8bd67d087c..97b5fca8966d 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -40,6 +40,9 @@
#include <linux/list.h>
#include <linux/mutex.h>

+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#include <drm/drm_device.h>
+#endif
#include <drm/drm_vma_manager.h>

struct iosys_map;
@@ -492,6 +495,36 @@ struct drm_gem_object {
DRM_GEM_FOPS,\
}

+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+int drm_gem_huge_mnt_create(struct drm_device *dev, const char *value);
+#else
+static inline int drm_gem_huge_mnt_create(struct drm_device *dev,
+ const char *value)
+{
+ return 0;
+}
+#endif
+
+/**
+ * drm_gem_get_huge_mnt - Get the huge tmpfs mountpoint used by a DRM device
+ * @dev: DRM device
+
+ * This function gets the huge tmpfs mountpoint used by DRM device @dev. A huge
+ * tmpfs mountpoint is used instead of `shm_mnt` after a successful call to
+ * drm_gem_huge_mnt_create() when CONFIG_TRANSPARENT_HUGEPAGE is enabled.
+
+ * Returns:
+ * The huge tmpfs mountpoint in use, NULL otherwise.
+ */
+static inline struct vfsmount *drm_gem_get_huge_mnt(struct drm_device *dev)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ return dev->huge_mnt;
+#else
+ return NULL;
+#endif
+}
+
void drm_gem_object_release(struct drm_gem_object *obj);
void drm_gem_object_free(struct kref *kref);
int drm_gem_object_init(struct drm_device *dev,
--
2.47.3