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Message-ID: <64e8708a-bb73-96ae-90af-f7b51317613b@collabora.com>
Date:   Tue, 26 Sep 2023 03:37:22 +0300
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Subject: Re: [PATCH v17 13/18] drm/shmem-helper: Add memory shrinker
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To:     Boris Brezillon <boris.brezillon@collabora.com>
Cc:     David Airlie <airlied@gmail.com>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        Qiang Yu <yuq825@gmail.com>,
        Steven Price <steven.price@arm.com>,
        Emma Anholt <emma@anholt.net>, Melissa Wen <mwen@igalia.com>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        kernel@collabora.com, virtualization@lists.linux-foundation.org
References: <20230914232721.408581-1-dmitry.osipenko@collabora.com>
 <20230914232721.408581-14-dmitry.osipenko@collabora.com>
 <20230915104633.0d5c3932@collabora.com>
From:   Dmitry Osipenko <dmitry.osipenko@collabora.com>
In-Reply-To: <20230915104633.0d5c3932@collabora.com>
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On 9/15/23 11:46, Boris Brezillon wrote:
>> -static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
>> +static int
>> +drm_gem_shmem_acquire_pages(struct drm_gem_shmem_object *shmem, bool init)
>>  {
>>  	struct drm_gem_object *obj = &shmem->base;
>>  	struct page **pages;
>>  
>>  	dma_resv_assert_held(shmem->base.resv);
>>  
>> -	if (refcount_inc_not_zero(&shmem->pages_use_count))
>> +	if (shmem->madv < 0) {
>> +		drm_WARN_ON(obj->dev, shmem->pages);
>> +		return -ENOMEM;
>> +	}
>> +
>> +	if (shmem->pages) {
>> +		drm_WARN_ON(obj->dev, !shmem->evicted);
>>  		return 0;
>> +	}
>> +
>> +	if (drm_WARN_ON(obj->dev, !(init ^ refcount_read(&shmem->pages_use_count))))
>> +		return -EINVAL;
> OOC, why do we care? Is there any difference between initial and re-pin
> that make the page allocation impossible? Feels like, if there's a
> check to do, it should be done in the caller instead, and you can drop
> the init param here.

This is a sanity check that addresses additional refcnt tracking
complexity imposed by shrinker.

This function is used by both init and re-pin that is invoked from
several places in the code. It's not trivial to move that check to the
callers.

-- 
Best regards,
Dmitry