[PATCH] drm/amdgpu: Adjust logic around GTT size (v3)

[Christian König]

Well the key point is it isn't better. It's just that different people 
will start complaining.

I'm fine with trying to change it once more, just keep in mind that we 
decide between two evils and somebody could start complaining.

Christian.

Am 14.06.22 um 15:43 schrieb Alex Deucher:
> I don't see how this is worse than the current behavior.  We have some
> bug reports where we have games that use a lot of memory and with the
> lower limit the system ends up dying due to swapping and the behavior
> is actually better with the patch.
>
> Alex
>
> On Thu, Jun 2, 2022 at 2:03 PM Christian König <christian.koenig at amd.com> wrote:
>> I totally agree on the reasoning, but I have the strong feeling that
>> this will blow up in our face once more.
>>
>> I've tried to raise this limit twice already and had to revert it both
>> times. And the reasons why I had to revert it haven't changed since them.
>>
>> Christian.
>>
>> Am 02.06.22 um 18:40 schrieb Alex Deucher:
>>> @Christian Koenig
>>> Any objections to this?  I realize that fixing the OOM killer is
>>> ultimately the right approach, but I don't really see how this makes
>>> things worse.  The current scheme is biased towards dGPUs as they have
>>> lots of on board memory so on dGPUs we can end up setting gtt size to
>>> 3/4 of system memory already in a lot of cases since there is often as
>>> much vram as system memory.  Due to the limits in ttm, we can't use
>>> more than half at the moment anway, so this shouldn't make things
>>> worse on dGPUs and would help a lot of APUs.  Once could make the
>>> argument that with more vram there is less need for gtt so less chance
>>> for OOM, but I think it is more of a scale issue.  E.g., on dGPUs
>>> you'll generally be running higher resolutions and texture quality,
>>> etc. so the overall memory footprint is just scaled up.
>>>
>>> Alex
>>>
>>> On Fri, May 20, 2022 at 11:09 AM Alex Deucher <alexander.deucher at amd.com> wrote:
>>>> Certain GL unit tests for large textures can cause problems
>>>> with the OOM killer since there is no way to link this memory
>>>> to a process.  This was originally mitigated (but not necessarily
>>>> eliminated) by limiting the GTT size.  The problem is this limit
>>>> is often too low for many modern games so just make the limit 1/2
>>>> of system memory. The OOM accounting needs to be addressed, but
>>>> we shouldn't prevent common 3D applications from being usable
>>>> just to potentially mitigate that corner case.
>>>>
>>>> Set default GTT size to max(3G, 1/2 of system ram) by default.
>>>>
>>>> v2: drop previous logic and default to 3/4 of ram
>>>> v3: default to half of ram to align with ttm
>>>>
>>>> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
>>>> ---
>>>>    drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 20 ++++++++++++++------
>>>>    1 file changed, 14 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>>> index d2b5cccb45c3..7195ed77c85a 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>>> @@ -1798,18 +1798,26 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
>>>>           DRM_INFO("amdgpu: %uM of VRAM memory ready\n",
>>>>                    (unsigned) (adev->gmc.real_vram_size / (1024 * 1024)));
>>>>
>>>> -       /* Compute GTT size, either bsaed on 3/4th the size of RAM size
>>>> +       /* Compute GTT size, either bsaed on 1/2 the size of RAM size
>>>>            * or whatever the user passed on module init */
>>>>           if (amdgpu_gtt_size == -1) {
>>>>                   struct sysinfo si;
>>>>
>>>>                   si_meminfo(&si);
>>>> -               gtt_size = min(max((AMDGPU_DEFAULT_GTT_SIZE_MB << 20),
>>>> -                              adev->gmc.mc_vram_size),
>>>> -                              ((uint64_t)si.totalram * si.mem_unit * 3/4));
>>>> -       }
>>>> -       else
>>>> +               /* Certain GL unit tests for large textures can cause problems
>>>> +                * with the OOM killer since there is no way to link this memory
>>>> +                * to a process.  This was originally mitigated (but not necessarily
>>>> +                * eliminated) by limiting the GTT size.  The problem is this limit
>>>> +                * is often too low for many modern games so just make the limit 1/2
>>>> +                * of system memory which aligns with TTM. The OOM accounting needs
>>>> +                * to be addressed, but we shouldn't prevent common 3D applications
>>>> +                * from being usable just to potentially mitigate that corner case.
>>>> +                */
>>>> +               gtt_size = max((AMDGPU_DEFAULT_GTT_SIZE_MB << 20),
>>>> +                              (u64)si.totalram * si.mem_unit / 2);
>>>> +       } else {
>>>>                   gtt_size = (uint64_t)amdgpu_gtt_size << 20;
>>>> +       }
>>>>
>>>>           /* Initialize GTT memory pool */
>>>>           r = amdgpu_gtt_mgr_init(adev, gtt_size);
>>>> --
>>>> 2.35.3
>>>>