Re: [PATCH v4 07/13] drm/v3d: Use huge tmpfs mount point helper

["Loïc Molinari" <loic.molinari@collabora.com>]

On 20/10/2025 11:33, Tvrtko Ursulin wrote:
> 
> On 15/10/2025 16:30, Loïc Molinari wrote:
>> Make use of the new drm_gem_huge_mnt_create() helper to avoid code
>> duplication. Now that it's just a few lines long, the single function
>> in v3d_gemfs.c is moved into v3d_gem.c.
>>
>> v3:
>> - use huge tmpfs mountpoint in drm_device
>> - move v3d_gemfs.c into v3d_gem.c
>>
>> v4:
>> - clean up mountpoint creation error handling
>>
>> Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
>> ---
>>   drivers/gpu/drm/v3d/Makefile    |  3 +-
>>   drivers/gpu/drm/v3d/v3d_bo.c    |  5 ++-
>>   drivers/gpu/drm/v3d/v3d_drv.c   |  2 +-
>>   drivers/gpu/drm/v3d/v3d_drv.h   | 11 +-----
>>   drivers/gpu/drm/v3d/v3d_gem.c   | 27 +++++++++++++--
>>   drivers/gpu/drm/v3d/v3d_gemfs.c | 60 ---------------------------------
>>   6 files changed, 30 insertions(+), 78 deletions(-)
>>   delete mode 100644 drivers/gpu/drm/v3d/v3d_gemfs.c
>>
>> diff --git a/drivers/gpu/drm/v3d/Makefile b/drivers/gpu/drm/v3d/Makefile
>> index fcf710926057..b7d673f1153b 100644
>> --- a/drivers/gpu/drm/v3d/Makefile
>> +++ b/drivers/gpu/drm/v3d/Makefile
>> @@ -13,8 +13,7 @@ v3d-y := \
>>       v3d_trace_points.o \
>>       v3d_sched.o \
>>       v3d_sysfs.o \
>> -    v3d_submit.o \
>> -    v3d_gemfs.o
>> +    v3d_submit.o
>>   v3d-$(CONFIG_DEBUG_FS) += v3d_debugfs.o
>> diff --git a/drivers/gpu/drm/v3d/v3d_bo.c b/drivers/gpu/drm/v3d/v3d_bo.c
>> index c41476ddde68..6b9909bfce82 100644
>> --- a/drivers/gpu/drm/v3d/v3d_bo.c
>> +++ b/drivers/gpu/drm/v3d/v3d_bo.c
>> @@ -112,7 +112,7 @@ v3d_bo_create_finish(struct drm_gem_object *obj)
>>       if (IS_ERR(sgt))
>>           return PTR_ERR(sgt);
>> -    if (!v3d->gemfs)
>> +    if (!obj->dev->huge_mnt)
> 
> Maybe it would be a good idea to add a helper for this check. Keeping 
> aligned with drm_gem_huge_mnt_create() something like 
> drm_gem_has_huge_mnt()? That would then hide the optional drm_device 
> struct member if you decide to go for that.

Sounds good. This would prevent cluttering code with ifdefs in drivers 
while still removing the huge_mnt field in drm_device in builds with 
CONFIG_TRANSPARENT_HUGEPAGE=n. I'll propose a new version doing so.

> 
>>           align = SZ_4K;
>>       else if (obj->size >= SZ_1M)
>>           align = SZ_1M;
>> @@ -148,12 +148,11 @@ struct v3d_bo *v3d_bo_create(struct drm_device 
>> *dev, struct drm_file *file_priv,
>>                    size_t unaligned_size)
>>   {
>>       struct drm_gem_shmem_object *shmem_obj;
>> -    struct v3d_dev *v3d = to_v3d_dev(dev);
>>       struct v3d_bo *bo;
>>       int ret;
>>       shmem_obj = drm_gem_shmem_create_with_mnt(dev, unaligned_size,
>> -                          v3d->gemfs);
>> +                          dev->huge_mnt);
> 
> Okay this one goes away by the end of the series.
> 
>>       if (IS_ERR(shmem_obj))
>>           return ERR_CAST(shmem_obj);
>>       bo = to_v3d_bo(&shmem_obj->base);
>> diff --git a/drivers/gpu/drm/v3d/v3d_drv.c b/drivers/gpu/drm/v3d/ 
>> v3d_drv.c
>> index c5a3bbbc74c5..19ec0ea7f38e 100644
>> --- a/drivers/gpu/drm/v3d/v3d_drv.c
>> +++ b/drivers/gpu/drm/v3d/v3d_drv.c
>> @@ -106,7 +106,7 @@ static int v3d_get_param_ioctl(struct drm_device 
>> *dev, void *data,
>>           args->value = v3d->perfmon_info.max_counters;
>>           return 0;
>>       case DRM_V3D_PARAM_SUPPORTS_SUPER_PAGES:
>> -        args->value = !!v3d->gemfs;
>> +        args->value = !!dev->huge_mnt;
>>           return 0;
>>       case DRM_V3D_PARAM_GLOBAL_RESET_COUNTER:
>>           mutex_lock(&v3d->reset_lock);
>> diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/ 
>> v3d_drv.h
>> index 1884686985b8..99a39329bb85 100644
>> --- a/drivers/gpu/drm/v3d/v3d_drv.h
>> +++ b/drivers/gpu/drm/v3d/v3d_drv.h
>> @@ -158,11 +158,6 @@ struct v3d_dev {
>>       struct drm_mm mm;
>>       spinlock_t mm_lock;
>> -    /*
>> -     * tmpfs instance used for shmem backed objects
>> -     */
>> -    struct vfsmount *gemfs;
>> -
>>       struct work_struct overflow_mem_work;
>>       struct v3d_queue_state queue[V3D_MAX_QUEUES];
>> @@ -569,6 +564,7 @@ extern const struct dma_fence_ops v3d_fence_ops;
>>   struct dma_fence *v3d_fence_create(struct v3d_dev *v3d, enum 
>> v3d_queue q);
>>   /* v3d_gem.c */
>> +extern bool super_pages;
>>   int v3d_gem_init(struct drm_device *dev);
>>   void v3d_gem_destroy(struct drm_device *dev);
>>   void v3d_reset_sms(struct v3d_dev *v3d);
>> @@ -576,11 +572,6 @@ void v3d_reset(struct v3d_dev *v3d);
>>   void v3d_invalidate_caches(struct v3d_dev *v3d);
>>   void v3d_clean_caches(struct v3d_dev *v3d);
>> -/* v3d_gemfs.c */
>> -extern bool super_pages;
>> -void v3d_gemfs_init(struct v3d_dev *v3d);
>> -void v3d_gemfs_fini(struct v3d_dev *v3d);
>> -
>>   /* v3d_submit.c */
>>   void v3d_job_cleanup(struct v3d_job *job);
>>   void v3d_job_put(struct v3d_job *job);
>> diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/ 
>> v3d_gem.c
>> index bb110d35f749..635ff0fabe7e 100644
>> --- a/drivers/gpu/drm/v3d/v3d_gem.c
>> +++ b/drivers/gpu/drm/v3d/v3d_gem.c
>> @@ -258,6 +258,30 @@ v3d_invalidate_caches(struct v3d_dev *v3d)
>>       v3d_invalidate_slices(v3d, 0);
>>   }
>> +static void
>> +v3d_huge_mnt_init(struct v3d_dev *v3d)
>> +{
>> +    int err = 0;
>> +
>> +    /*
>> +     * By using a huge shmemfs mountpoint when the user wants to
>> +     * enable Super Pages, we can pass in mount flags that better
>> +     * match our usecase.
>> +     */
>> +
>> +    if (super_pages)
>> +        err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
> 
> If it is this patch that is creating the build failure then the two 
> should be squashed.
> 
> Then in "drm/v3d: Fix builds with CONFIG_TRANSPARENT_HUGEPAGE=n" this 
> ends up a bit ugly:
> 
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>       if (super_pages)
> #endif
>           err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
> 
> Does this not work:
> 
>       if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && super_pages)
>           err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
> 
> ?

I've got a new version ready that does exactly that (after discussing 
with Boris).

> 
> Regards,
> 
> Tvrtko
> 
>> +
>> +    if (v3d->drm.huge_mnt)
>> +        drm_info(&v3d->drm, "Using Transparent Hugepages\n");
>> +    else if (err)
>> +        drm_warn(&v3d->drm, "Can't use Transparent Hugepages (%d)\n",
>> +             err);
>> +    else
>> +        drm_notice(&v3d->drm,
>> +               "Transparent Hugepage support is recommended for 
>> optimal performance on this platform!\n");
>> +}
>> +
>>   int
>>   v3d_gem_init(struct drm_device *dev)
>>   {
>> @@ -309,7 +333,7 @@ v3d_gem_init(struct drm_device *dev)
>>       v3d_init_hw_state(v3d);
>>       v3d_mmu_set_page_table(v3d);
>> -    v3d_gemfs_init(v3d);
>> +    v3d_huge_mnt_init(v3d);
>>       ret = v3d_sched_init(v3d);
>>       if (ret) {
>> @@ -329,7 +353,6 @@ v3d_gem_destroy(struct drm_device *dev)
>>       enum v3d_queue q;
>>       v3d_sched_fini(v3d);
>> -    v3d_gemfs_fini(v3d);
>>       /* Waiting for jobs to finish would need to be done before
>>        * unregistering V3D.
>> diff --git a/drivers/gpu/drm/v3d/v3d_gemfs.c b/drivers/gpu/drm/v3d/ 
>> v3d_gemfs.c
>> deleted file mode 100644
>> index c1a30166c099..000000000000
>> --- a/drivers/gpu/drm/v3d/v3d_gemfs.c
>> +++ /dev/null
>> @@ -1,60 +0,0 @@
>> -// SPDX-License-Identifier: GPL-2.0+
>> -/* Copyright (C) 2024 Raspberry Pi */
>> -
>> -#include <linux/fs.h>
>> -#include <linux/mount.h>
>> -#include <linux/fs_context.h>
>> -
>> -#include "v3d_drv.h"
>> -
>> -void v3d_gemfs_init(struct v3d_dev *v3d)
>> -{
>> -    struct file_system_type *type;
>> -    struct fs_context *fc;
>> -    struct vfsmount *gemfs;
>> -    int ret;
>> -
>> -    /*
>> -     * 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;
>> -
>> -    /* The user doesn't want to enable Super Pages */
>> -    if (!super_pages)
>> -        goto err;
>> -
>> -    type = get_fs_type("tmpfs");
>> -    if (!type)
>> -        goto err;
>> -
>> -    fc = fs_context_for_mount(type, SB_KERNMOUNT);
>> -    if (IS_ERR(fc))
>> -        goto err;
>> -    ret = vfs_parse_fs_string(fc, "source", "tmpfs");
>> -    if (!ret)
>> -        ret = vfs_parse_fs_string(fc, "huge", "within_size");
>> -    if (!ret)
>> -        gemfs = fc_mount_longterm(fc);
>> -    put_fs_context(fc);
>> -    if (ret)
>> -        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);
>> -}
>