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Message-ID: <9d9e745d-a417-d07f-e413-095dd2f610ac@collabora.com>
Date:   Mon, 14 Nov 2022 20:13:31 +0300
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Subject: Re: [PATCH v8 7/7] drm/panfrost: Switch to generic memory shrinker
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To:     Steven Price <steven.price@arm.com>,
        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>,
        Gustavo Padovan <gustavo.padovan@collabora.com>,
        Daniel Stone <daniel@fooishbar.org>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Rob Clark <robdclark@gmail.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        Qiang Yu <yuq825@gmail.com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>,
        Rob Herring <robh@kernel.org>, Sean Paul <sean@poorly.run>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        Dmitry Osipenko <digetx@gmail.com>, kernel@collabora.com,
        virtualization@lists.linux-foundation.org
References: <20221105232719.302619-1-dmitry.osipenko@collabora.com>
 <20221105232719.302619-8-dmitry.osipenko@collabora.com>
 <41c4d78c-cb47-d06f-f6af-e827dd56b857@arm.com>
From:   Dmitry Osipenko <dmitry.osipenko@collabora.com>
In-Reply-To: <41c4d78c-cb47-d06f-f6af-e827dd56b857@arm.com>
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Hello Steve,

On 11/14/22 19:54, Steven Price wrote:
> On 05/11/2022 23:27, Dmitry Osipenko wrote:
>> Replace Panfrost's custom memory shrinker with a common drm-shmem
>> memory shrinker.
>>
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> 
> Sadly this triggers GPU faults under memory pressure - it looks
> suspiciously like mappings are being freed while the jobs are still running.
> 
> I'm not sure I understand how the generic shrinker replicates the
> "gpu_usecount" atomic that Panfrost currently has, and I'm wondering if
> that's the cause?
> 
> Also just reverting this commit (so just patches 1-6) I can't actually
> get Panfrost to purge any memory. So I don't think the changes (most
> likely in patch 4) are quite right either.
> 
> At the moment I don't have the time to investigate in detail. But if
> you've any ideas for something specific I should look at I can run more
> testing.

Thank you for the testing! It just occurred to me that the shrinker
callback lost the dma_resv_test_signaled() in comparison to the previous
versions of this patchset. It appeared to me that the drm_gem_lru now
checks whether reservation is busy, but it doesn't.

I saw a similar page faults once in a while when was testing the
Panfrost driver, but then couldn't reproduce the faults after applying
the IOMMU unmap range fix that Robin made recently.

I'll re-add the dma_resv_test_signaled() in v9, it was a luck that I
didn't hit it much during my testing.

-- 
Best regards,
Dmitry