linux-kernel - Re: [PATCH v4 08/13] drm/v3d: Fix builds with CONFIG_TRANSPARENT

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Message-ID: <efc1d805-1613-45a9-aa15-fcc009adf27c@collabora.com>
Date: Wed, 15 Oct 2025 22:41:59 +0200
From: Loïc Molinari <loic.molinari@...labora.com>
To: Boris Brezillon <boris.brezillon@...labora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Tvrtko Ursulin
 <tursulin@...ulin.net>, Rob Herring <robh@...nel.org>,
 Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>,
 Melissa Wen <mwen@...lia.com>, Maíra Canal
 <mcanal@...lia.com>, Hugh Dickins <hughd@...gle.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Al Viro
 <viro@...iv.linux.org.uk>, Mikołaj Wasiak
 <mikolaj.wasiak@...el.com>, Christian Brauner <brauner@...nel.org>,
 Nitin Gote <nitin.r.gote@...el.com>, Andi Shyti
 <andi.shyti@...ux.intel.com>, Jonathan Corbet <corbet@....net>,
 Christopher Healy <healych@...zon.com>, Matthew Wilcox
 <willy@...radead.org>, Bagas Sanjaya <bagasdotme@...il.com>,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 intel-gfx@...ts.freedesktop.org, linux-mm@...ck.org,
 linux-doc@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH v4 08/13] drm/v3d: Fix builds with
 CONFIG_TRANSPARENT_HUGEPAGE=n

On 15/10/2025 20:17, Boris Brezillon wrote:
> On Wed, 15 Oct 2025 17:30:12 +0200
> Loïc Molinari <loic.molinari@...labora.com> 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 <loic.molinari@...labora.com>
>> ---
>>   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?

> 
>>   
>>   	if (v3d->drm.huge_mnt)
>