On 15/10/2025 16:30, Loïc Molinari wrote:
Add the drm_gem_huge_mnt_create() helper to avoid code duplication in
the i915, V3D, Panfrost and Panthor drivers. It creates and mounts a
dedicated huge tmpfs mountpoint, for the lifetime of a DRM device,
used at GEM object initialization.
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
Signed-off-by: Loïc Molinari <[email protected]>
---
drivers/gpu/drm/drm_gem.c | 58 +++++++++++++++++++++++++++++++++++++++
include/drm/drm_device.h | 11 ++++++++
include/drm/drm_gem.h | 1 +
3 files changed, 70 insertions(+)
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index a98d5744cc6c..db8c0a217add 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -29,6 +29,7 @@
#include <linux/export.h>
#include <linux/file.h>
#include <linux/fs.h>
+#include <linux/fs_context.h>
#include <linux/iosys-map.h>
#include <linux/mem_encrypt.h>
#include <linux/mm.h>
@@ -82,6 +83,63 @@
* up at a later date, and as our interface with shmfs for memory allocation.
*/
+static void drm_gem_huge_mnt_free(struct drm_device *dev, void *data)
+{
+ drm_WARN_ON(dev, dev->huge_mnt == NULL);
I don't see a benefit of adding this check but maybe I am missing something.
+
+ kern_unmount(dev->huge_mnt);
+ dev->huge_mnt = NULL;
Ditto - device is going away, no? So why bother clearing the pointer?
Also, is the compiler smart enough to not compile or complain this
function is unused in the !CONFIG_TRANSPARENT_HUGEPAGE case?
+}
+
+/**
+ * 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.
+ */
+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 (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+ return 0;
Is there a specific reason why the !CONFIG_TRANSPARENT_HUGEPAGE path is
not implemented in the header as a static inline? That would enable
those builds to avoid the pointless function in text and function call
in the drivers.
+ if (unlikely(dev->huge_mnt))
+ return 0;
Any special reason why it is allowed to call it multiple times with success?
+
+ 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);
+
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..352e3db402d7 100644
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -3,6 +3,7 @@
#include <linux/list.h>
#include <linux/kref.h>
+#include <linux/mount.h>
#include <linux/mutex.h>
#include <linux/idr.h>
#include <linux/sched.h>
@@ -168,6 +169,16 @@ 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.
+ */
+ struct vfsmount *huge_mnt;
Maybe it would be nice to hide this in the !CONFIG_TRANSPARENT_HUGEPAGE
case? A bit ugly to add an ifdef but it is also a bit questionable to
force the member on everyone.
Regards,
Tvrtko
+
/**
* @driver_features: per-device driver features
*
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 7c8bd67d087c..7285a62d9afc 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -492,6 +492,7 @@ struct drm_gem_object {
DRM_GEM_FOPS,\
}
+int drm_gem_huge_mnt_create(struct drm_device *dev, const char *value);
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,
