drm/v3d: Introduce gemfs

Create a separate "tmpfs" kernel mount for V3D. This will allow us to
move away from the shmemfs `shm_mnt` and gives the flexibility to do
things like set our own mount options. Here, the interest is to use
"huge=", which should allow us to enable the use of THP for our
shmem-backed objects.

Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240923141348.2422499-6-mcanal@igalia.com

1 files changed, 46 insertions, 0 deletions

diff --git a/drivers/gpu/drm/v3d/v3d_gemfs.c b/drivers/gpu/drm/v3d/v3d_gemfs.c
new file mode 100644
index 000000000000..31cf5bd11e39
--- /dev/null
+++ b/drivers/gpu/drm/v3d/v3d_gemfs.c
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* Copyright (C) 2024 Raspberry Pi */
+
+#include <linux/fs.h>
+#include <linux/mount.h>
+
+#include "v3d_drv.h"
+
+void v3d_gemfs_init(struct v3d_dev *v3d)
+{
+	char huge_opt[] = "huge=within_size";
+	struct file_system_type *type;
+	struct vfsmount *gemfs;
+
+	/*
+	 * By creating our own shmemfs mountpoint, we can pass in
+	 * mount flags that better match our usecase. However, we
+	 * only do so on platforms which benefit from it.
+	 */
+	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+		goto err;
+
+	type = get_fs_type("tmpfs");
+	if (!type)
+		goto err;
+
+	gemfs = vfs_kern_mount(type, SB_KERNMOUNT, type->name, huge_opt);
+	if (IS_ERR(gemfs))
+		goto err;
+
+	v3d->gemfs = gemfs;
+	drm_info(&v3d->drm, "Using Transparent Hugepages\n");
+
+	return;
+
+err:
+	v3d->gemfs = NULL;
+	drm_notice(&v3d->drm,
+		   "Transparent Hugepage support is recommended for optimal performance on this platform!\n");
+}
+
+void v3d_gemfs_fini(struct v3d_dev *v3d)
+{
+	if (v3d->gemfs)
+		kern_unmount(v3d->gemfs);
+}