Hi Boris,
On 16/10/2025 07:56, Boris Brezillon wrote:
On Wed, 15 Oct 2025 22:41:59 +0200
Loïc Molinari <[email protected]> wrote:
On 15/10/2025 20:17, Boris Brezillon wrote:
On Wed, 15 Oct 2025 17:30:12 +0200
Loïc Molinari <[email protected]> wrote:
Don't declare "super_pages" on builds with CONFIG_TRANSPARENT_HUGEPAGE
disabled to prevent build error:
ERROR: modpost: "super_pages" [drivers/gpu/drm/v3d/v3d.ko] undefined!
I believe this is a bug introduced by the previous commit: the
compiler probably drops any code between the
IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) check and the err label
because IS_ENABLED() evaluates to false at compile time. So I'd squash
those changes in the previous commit.
Right, it's been introduced in previous commit.
Signed-off-by: Loïc Molinari <[email protected]>
---
drivers/gpu/drm/v3d/v3d_drv.h | 2 ++
drivers/gpu/drm/v3d/v3d_gem.c | 2 ++
2 files changed, 4 insertions(+)
diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h
index 99a39329bb85..481502104391 100644
--- a/drivers/gpu/drm/v3d/v3d_drv.h
+++ b/drivers/gpu/drm/v3d/v3d_drv.h
@@ -564,7 +564,9 @@ 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 */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
extern bool super_pages;
+#endif
int v3d_gem_init(struct drm_device *dev);
void v3d_gem_destroy(struct drm_device *dev);
void v3d_reset_sms(struct v3d_dev *v3d);
diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
index 635ff0fabe7e..0039063eb8b2 100644
--- a/drivers/gpu/drm/v3d/v3d_gem.c
+++ b/drivers/gpu/drm/v3d/v3d_gem.c
@@ -269,7 +269,9 @@ v3d_huge_mnt_init(struct v3d_dev *v3d)
* match our usecase.
*/
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
if (super_pages)
+#endif
err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
Why not
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
if (super_pages)
err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
#endif
I guess
if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && super_pages)
err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
would also do, since it's likely to rely on the same optimization the
previous v3d_gemfs_init() implementation was relying on, but it's
fragile (not sure what happens when compiled with -O0).
I'll remove the #ifdef/#endif around the super_pages declaration in
v3d_drv.h because it isn't necessary if super_pages is compiled out in
v3d_huge_mnt_init().
In v3d_huge_mnt_init(), I'd add the #ifdef before the ret variable
declaration and the #endif right after the last else so that it's clear
drm_notice("THP is recommended...") is called unconditionally when
CONFIG_TRANSPARENT_HUGEPAGE=n, whatever the optim level. What do you think?
First off, I'm not a huge fan of the following pattern
#if foo
if (xxxx)
#endif
do_something
which also applies to
#if foo
if (xxxx)
do_xxx
else if (yyy)
do_yyy
else
#endif
do_something
I'd rather have do_something duplicated in an #else section
like that:
#if foo
if (xxxx)
do_xxx
else if (yyy)
do_yyy
else
do_something
#else
do_something
#endif
But I'm not even seeing what the problem is here. If you do:
int err = 0;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
if (super_pages)
err = drm_gem_huge_mnt_create(&v3d->drm, "within_size");
#endif
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");
You're guaranteed that err=0 and v3d->drm.huge_mnt=NULL when
CONFIG_TRANSPARENT_HUGEPAGE=n, so the "THP recommended"
message should be displayed unconditionally. Am I missing
something?
It doesn't really matter here but I just thought it would be cleaner to
explicitly let just the drm_notice() because the compiler doesn't know
v3d->drm.huge_mnt is always NULL here and would emit a branch in
CONFIG_TRANSPARENT_HUGEPAGE=n builds. I know your dislike for this
pattern now, so I will stick to the suggestion :)
Loïc
