Re: [PATCH 3/3] drm/i915/gtt: ignore min_page_size for paging structures

From: Matthew Auld <matthew.auld@intel.com>
To: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>,
	intel-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 3/3] drm/i915/gtt: ignore min_page_size for paging structures
Date: Wed, 23 Jun 2021 14:38:14 +0100	[thread overview]
Message-ID: <fbb13fc4-18bb-8e92-71b6-7a4a7d84b633@intel.com> (raw)
In-Reply-To: <62c8a7a3-dcdd-ec6d-a976-7203e406d364@linux.intel.com>

On 23/06/2021 14:32, Thomas Hellström wrote:
> 
> On 6/23/21 1:26 PM, Matthew Auld wrote:
>> The min_page_size is only needed for pages inserted into the GTT, and
>> for our paging structures we only need at most 4K bytes, so simply
>> ignore the min_page_size restrictions here, otherwise we might see some
>> severe overallocation on some devices.
>>
>> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
>> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>> ---
>>   drivers/gpu/drm/i915/gt/intel_gtt.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.c 
>> b/drivers/gpu/drm/i915/gt/intel_gtt.c
>> index 084ea65d59c0..61e8a8c25374 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_gtt.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_gtt.c
>> @@ -16,7 +16,7 @@ struct drm_i915_gem_object *alloc_pt_lmem(struct 
>> i915_address_space *vm, int sz)
>>   {
>>       struct drm_i915_gem_object *obj;
>> -    obj = i915_gem_object_create_lmem(vm->i915, sz, 0);
>> +    obj = __i915_gem_object_create_lmem_with_ps(vm->i915, sz, sz, 0);
> 
> So is this memory always required to be size aligned? or should it say 
> sz, PAGE_SIZE?

The scratch page also hits this path, which is another can of worms. In 
terms of size it might need to be 64K(with proper physical alignment), 
which is why we can't force 4K here, and instead need to use the passed 
in size, where the returned page will have the same alignment.

> 
> /Thomas
> 
> 