[PATCH v5 05/12] drm/gem: Add huge tmpfs mountpoint helpers

Loïc Molinari
2025-10-21T11:31:02Z

Add the drm_gem_huge_mnt_create() and drm_gem_has_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 checks whether a dedicated huge tmpfs
mountpoint is in use by a DRM device.

The next commits will port drivers to this helper.

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:
- removed 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

Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
---
drivers/gpu/drm/drm_gem.c | 39 +++++++++++++++++++++++++++++
include/drm/drm_device.h | 15 +++++++++++
include/drm/drm_gem.h | 52 +++++++++++++++++++++++++++++++++++++++
3 files changed, 106 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index a98d5744cc6c..161da048330e 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 +85,42 @@
* 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);
+}
+
+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_has_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 778b2cca6c49..684939987d83 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;

+ /**
+ * @huge_mnt:
+ *
+ * Huge tmpfs mountpoint used at GEM object initialization
+ * drm_gem_object_init(). Drivers can call drm_gem_huge_mnt_create() to
+ * create a huge tmfps mountpoint. The default tmpfs mountpoint
+ * (`shm_mnt`) is used if NULL.
+ */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ 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..9845854850fb 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -492,6 +492,58 @@ struct drm_gem_object {
DRM_GEM_FOPS,\
}

+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+int __drm_gem_huge_mnt_create(struct drm_device *dev, const char *value);
+#endif
+
+/**
+ * drm_gem_huge_mnt_create - Create, mount and use a huge tmpfs mountpoint
+ * @dev: DRM device a huge tmpfs mountpoint should be used with
+ * @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 value @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.
+ */
+static inline int drm_gem_huge_mnt_create(struct drm_device *dev,
+ const char *value)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ return __drm_gem_huge_mnt_create(dev, value);
+#else
+ return 0;
+#endif
+}
+
+/**
+ * drm_gem_has_huge_mnt - Check if a huge tmpfs mountpoint is in use
+ * @dev: DRM device
+ *
+ * This function checks whether a huge tmpfs mountpoint is in use after by DRM
+ * device @dev. A huge tmpfs mountpoint is used after a successful call to
+ * drm_gem_huge_mnt_create() on builds with Transparent Hugepage enabled.
+ *
+ * Returns:
+ * true on success, false otherwise.
+ */
+static inline bool drm_gem_has_huge_mnt(struct drm_device *dev)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ return !!dev->huge_mnt;
+#else
+ return false;
+#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