Re: [PATCH 2/5] drm/gem: Add a mountpoint parameter to drm_gem_object_init()

From: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
To: "Christian König" <christian.koenig@amd.com>,
	"Maíra Canal" <mcanal@igalia.com>,
	"Melissa Wen" <mwen@igalia.com>, "Iago Toral" <itoral@igalia.com>,
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	"Maxime Ripard" <mripard@kernel.org>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"David Airlie" <airlied@gmail.com>,
	"Daniel Vetter" <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org, kernel-dev@igalia.com,
	"Russell King" <linux@armlinux.org.uk>,
	"Lucas Stach" <l.stach@pengutronix.de>,
	"Christian Gmeiner" <christian.gmeiner@gmail.com>,
	"Inki Dae" <inki.dae@samsung.com>,
	"Seung-Woo Kim" <sw0312.kim@samsung.com>,
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	"Karolina Stolarek" <karolina.stolarek@intel.com>,
	"Andi Shyti" <andi.shyti@linux.intel.com>
Subject: Re: [PATCH 2/5] drm/gem: Add a mountpoint parameter to drm_gem_object_init()
Date: Tue, 12 Mar 2024 09:30:11 +0000	[thread overview]
Message-ID: <07885e3b-ee7b-456b-9fad-17d9009a4cb7@igalia.com> (raw)
In-Reply-To: <3a5d07c0-120f-47f9-a35a-31f3bfcc9330@amd.com>

On 12/03/2024 08:59, Christian König wrote:
> Am 12.03.24 um 09:51 schrieb Tvrtko Ursulin:
>>
>> Hi Maira,
>>
>> On 11/03/2024 10:05, Maíra Canal wrote:
>>> For some applications, such as using huge pages, we might want to have a
>>> different mountpoint, for which we pass in mount flags that better match
>>> our usecase.
>>>
>>> Therefore, add a new parameter to drm_gem_object_init() that allow us to
>>> define the tmpfs mountpoint where the GEM object will be created. If
>>> this parameter is NULL, then we fallback to shmem_file_setup().
>>
>> One strategy for reducing churn, and so the number of drivers this 
>> patch touches, could be to add a lower level drm_gem_object_init() 
>> (which takes vfsmount, call it __drm_gem_object_init(), or 
>> drm__gem_object_init_mnt(), and make drm_gem_object_init() call that 
>> one with a NULL argument.
> 
> I would even go a step further into the other direction. The shmem 
> backed GEM object is just some special handling as far as I can see.
> 
> So I would rather suggest to rename all drm_gem_* function which only 
> deal with the shmem backed GEM object into drm_gem_shmem_*.

That makes sense although it would be very churny. I at least would be 
on the fence regarding the cost vs benefit.

> Also the explanation why a different mount point helps with something 
> isn't very satisfying.

Not satisfying as you think it is not detailed enough to say driver 
wants to use huge pages for performance? Or not satisying as you 
question why huge pages would help?

Regards,

Tvrtko