linux-kernel - Re: [PATCH v1 5/5] drm/virtio: Add memory shrinker

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Date:   Wed, 9 Mar 2022 14:55:36 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Rob Clark <robdclark@...il.com>
Cc:     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>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Dmitry Osipenko <digetx@...il.com>
Subject: Re: [PATCH v1 5/5] drm/virtio: Add memory shrinker


On 3/9/22 04:12, Rob Clark wrote:
>> +static unsigned long
>> +virtio_gpu_gem_shrinker_count_objects(struct shrinker *shrinker,
>> +                                     struct shrink_control *sc)
>> +{
>> +       struct drm_gem_shmem_object *shmem;
>> +       struct virtio_gpu_device *vgdev;
>> +       unsigned long count = 0;
>> +       bool empty = true;
>> +
>> +       vgdev = container_of(shrinker, struct virtio_gpu_device,
>> +                            vgshrinker.shrinker);
>> +
>> +       if (!mutex_trylock(&vgdev->mm_lock))
>> +               return 0;
> One bit of advice from previously dealing with shrinker and heavy
> memory pressure situations (turns out 4GB chromebooks can be pretty
> much under *constant* memory pressure):
> 
> You *really* want to make shrinker->count_objects lockless.. and
> minimize the lock contention on shrinker->scan_objects (ie.  The
> problem is you can end up with shrinking going on on all CPU cores in
> parallel, you want to not funnel that thru one lock as much as
> possible.
> 
> See in particular:
> 
> 25ed38b3ed26 ("drm/msm: Drop mm_lock in scan loop")
> cc8a4d5a1bd8 ("drm/msm: Avoid mutex in shrinker_count()")

Thank you, I'll take that into account for v2.