linux-kernel - Re: [PATCH v2 8/8] drm/panfrost: Switch to generic memory shrinker

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Message-ID: <bdfbe26c-2071-1586-f2a7-0c4a9ed52451@collabora.com>
Date:   Fri, 18 Mar 2022 20:09:04 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Steven Price <steven.price@....com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Daniel Stone <daniel@...ishbar.org>,
        virtualization@...ts.linux-foundation.org,
        Dmitry Osipenko <digetx@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Daniel Almeida <daniel.almeida@...labora.com>,
        Gert Wollny <gert.wollny@...labora.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Rob Herring <robh@...nel.org>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
Subject: Re: [PATCH v2 8/8] drm/panfrost: Switch to generic memory shrinker

On 3/18/22 17:47, Steven Price wrote:
> On 18/03/2022 14:41, Dmitry Osipenko wrote:
>>
>> On 3/17/22 02:04, Dmitry Osipenko wrote:
>>>
>>> On 3/16/22 18:04, Steven Price wrote:
>>>> On 14/03/2022 22:42, Dmitry Osipenko wrote:
>>>>> Replace Panfrost's memory shrinker with a generic DRM memory shrinker.
>>>>>
>>>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
>>>>> ---
>>>> I gave this a spin on my Firefly-RK3288 board and everything seems to
>>>> work. So feel free to add a:
>>>>
>>>> Tested-by: Steven Price <steven.price@....com>
>>>>
>>>> As Alyssa has already pointed out you need to remove the
>>>> panfrost_gem_shrinker.c file. But otherwise everything looks fine, and
>>>> I'm very happy to see the shrinker code gone ;)
>>>
>>> Awesome, thank you.
>>
>> Steven, could you please tell me how exactly you tested the shrinker?
>>
>> I realized that today's IGT doesn't have any tests for the Panfrost's
>> madvise ioctl.
>>
>> You may invoke "echo 2 > /proc/sys/vm/drop_caches" manually in order to
>> trigger shrinker while 3d app is running actively (like a game or
>> benchmark). Nothing crashing will be a good enough indicator that it
>> works okay.
>>
>> I may get an RK board next week and then will be able to test it by
>> myself, so please don't hurry.
> 
> I have to admit it wasn't a very thorough test. I run glmark on the
> board with the following hack:
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index b014dadcf51f..194dec00695a 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -279,6 +279,14 @@ static int panfrost_ioctl_submit(struct drm_device *dev, void *data,
>         if (ret)
>                 goto out_cleanup_job;
>  
> +       {
> +       struct shrink_control sc = {
> +               .nr_to_scan = 1000
> +       };
> +       dev->shmem_shrinker->base.scan_objects(&dev->shmem_shrinker->base,
> +                       &sc);
> +       }
> +
>         ret = panfrost_job_push(job);
>         if (ret)
>                 goto out_cleanup_job;
> 
> That hack was specifically because I had some doubts about the removal
> of the 'gpu_usecount' counter and wanted to ensure that purging as the
> job is submitted wouldn't cause problems.
> 
> The drop_caches file should also work AFAIK.

Yours variant of testing looks okay, thanks.

We check BO's reservation dma-fence status in the shrinker's scan(), so
BO won't be purged until the last job has completed using the BO. The
'gpu_usecount' is redundant now, and thus, I removed it.