linux-kernel - Re: [PATCH v8 4/7] drm/shmem-helper: Add memory shrinker

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Message-ID: <f2d96471-5c72-1529-2e82-382260335aad@collabora.com>
Date:   Wed, 9 Nov 2022 21:48:11 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Dmitry Osipenko <digetx@...il.com>, kernel@...labora.com,
        virtualization@...ts.linux-foundation.org,
        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>,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Daniel Stone <daniel@...ishbar.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Qiang Yu <yuq825@...il.com>,
        Steven Price <steven.price@....com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Rob Herring <robh@...nel.org>, Sean Paul <sean@...rly.run>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>
Subject: Re: [PATCH v8 4/7] drm/shmem-helper: Add memory shrinker

Hello Thomas,

On 11/9/22 13:28, Thomas Zimmermann wrote:
>> +int drm_gem_shmem_set_evictable(struct drm_gem_shmem_object *shmem)
>> +{
>> +    dma_resv_lock(shmem->base.resv, NULL);
>> +
>> +    if (shmem->madv < 0) {
>> +        dma_resv_unlock(shmem->base.resv);
>> +        return -ENOMEM;
> 
> ENOMEM is not right here. It's for failed memory allocation. ENODEV
> seems more appropriate.

Had the same thought about ENOMEM and at one point was considering
ENOENT, but in the end decided it's not much better than ENOMEM.

> But why do we need an error here anyway? Why not just fail transparently?

I added the error handling everywhere for consistency. Perhaps indeed
will be better to fail transparently for now since nobody cares about
such errors and likely won't in the future.

The rest of the comments are also good to me, will start preparing the
v9. Thank you for the review!

-- 
Best regards,
Dmitry