linux-kernel - Re: [PATCH v2 7/8] drm/virtio: Support memory shrinking

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Date:   Wed, 16 Mar 2022 17:23:49 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Emil Velikov <emil.l.velikov@...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>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Rob Herring <robh@...nel.org>,
        Steven Price <steven.price@....com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        Dmitry Osipenko <digetx@...il.com>
Subject: Re: [PATCH v2 7/8] drm/virtio: Support memory shrinking

On 3/15/22 15:43, Emil Velikov wrote:
> Greetings everyone,
> 
> Food for thought: Would it make sense to have the madvise ioctl as
> generic DRM one?
> Looking around - i915, msm & panfrost already have one and the virtio
> implementation [below] seems as generic as it gets.
> 
> On Mon, 14 Mar 2022 at 22:44, Dmitry Osipenko
> <dmitry.osipenko@...labora.com> wrote:
> 
>> +#define VIRTGPU_MADV_WILLNEED 0
>> +#define VIRTGPU_MADV_DONTNEED 1
>> +struct drm_virtgpu_madvise {
>> +       __u32 bo_handle;
>> +       __u32 retained; /* out, non-zero if BO can be used */
>> +       __u32 madv;
>> +       __u32 pad;
> 
> This seems to be based on panfrost/msm yet names (bo_handle vs
> handle), layout and documentation varies.
> Why is that - copy/paste is cheap :-P

Indeed, there is copy/pasting among drivers. But I'm doubtful about
making madvise a generic ioctl because some drivers already have own
ioctl for that and h/w capabilities vary, so some drivers may want to
have extra features later on and then this doesn't feel like a common
thing anymore.