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Date:   Tue, 15 Mar 2022 02:04:57 +0300
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Subject: Re: [PATCH v1 0/5] Add memory shrinker to VirtIO-GPU DRM driver
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From:   Dmitry Osipenko <dmitry.osipenko@collabora.com>
To:     Rob Clark <robdclark@gmail.com>
Cc:     David Airlie <airlied@linux.ie>, Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        Daniel Almeida <daniel.almeida@collabora.com>,
        Gert Wollny <gert.wollny@collabora.com>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@lists.linux-foundation.org>,
        Gustavo Padovan <gustavo.padovan@collabora.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Dmitry Osipenko <digetx@gmail.com>,
        Rob Clark <robdclark@chromium.org>
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On 3/10/22 01:43, Dmitry Osipenko wrote:
>> I think that, given virgl uses host storage, guest shrinker should be
>> still useful.. so I think continue with this series.
> Guest shrinker indeed will be useful for virgl today. I was already
> questioning why virgl needs both host and guest storages, maybe it will
> move to a host-only storage approach in the future.
> 
> I think the variant with the timer expiration actually could be
> interesting to try because it should allow host to purge its VM BOs by
> itself, preventing host OOMs.

While I was working on shrinker v2, I noticed that host-side allocation
may take a significant time. So I decided to defer implementation of my
idea of using timer-based expiration for host-only BOs. I'll need to
examine it more.

>> For host shrinker, I'll have to look more at when crosvm triggers
>> balloon inflation.  I could still go the MADV:WILLNEED_REPLACE
>> approach instead, which does have the advantage of host kernel not
>> relying on host userspace or vm having a chance to run in order to
>> release pages.  The downside (perhaps?) is it would be more specific
>> to virtgpu-native-context and less so to virgl or venus (but I guess
>> there doesn't currently exist a way for madvise to be useful for vk
>> drivers).
> I'll also take a look at what CrOS does, maybe it has some interesting
> ideas.

I looked at CrOS kernel and crosvm, and haven't noticed anything special
there in regards to purging GPU's memory of VM on host-side memory
pressure. If you'll find something, then please let me know.

I sent out v2 of the shrinker series, but missed to CC you on it by
accident, please find it here [1].

[1]
https://lore.kernel.org/dri-devel/20220314224253.236359-1-dmitry.osipenko@collabora.com/T/#t