linux-kernel - Re: [PATCH v2 6/8] drm/shmem-helper: Add generic memory shrinker

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Message-ID: <aa3545cd-03c6-d45c-8b2c-9779e8327a55@collabora.com>
Date:   Thu, 17 Mar 2022 20:45:33 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     David Airlie <airlied@...ux.ie>, Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>,
        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>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Daniel Stone <daniel@...ishbar.org>,
        virtualization@...ts.linux-foundation.org,
        Dmitry Osipenko <digetx@...il.com>
Subject: Re: [PATCH v2 6/8] drm/shmem-helper: Add generic memory shrinker

On 3/17/22 20:32, Daniel Vetter wrote:
>> +static void drm_gem_shmem_update_purgeable_status(struct drm_gem_shmem_object *shmem)
>> +{
>> +	struct drm_gem_object *obj = &shmem->base;
>> +	struct drm_gem_shmem_shrinker *gem_shrinker = obj->dev->shmem_shrinker;
>> +	size_t page_count = obj->size >> PAGE_SHIFT;
>> +
>> +	if (!gem_shrinker || obj->import_attach || !obj->funcs->purge)
>> +		return;
>> +
>> +	mutex_lock(&shmem->vmap_lock);
>> +	mutex_lock(&shmem->pages_lock);
>> +	mutex_lock(&gem_shrinker->lock);
> Uh this is just terrible I think.
> 
> Can't we move shmem helpers over to reasonable locking, i.e. per-object
> dma_resv_lock for everything? I know it's a pile of work, but I think
> we're way past the point with things like this popping up where we should
> just bite that bullet.
> 
> I discussed the full thing with Daniel Stone, but maybe a joint refresher
> on irc would be a good thing.

Aha! Perhaps I saw bits of that discussion, but it wasn't entirely clear
to me what was discussed in fact. Sounds like a good idea to try to use
the reservation lock everywhere, thank you for the suggestion.