linux-kernel - Re: [PATCH v3 09/15] drm/gem: Add LRU/shrinker helper

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Date:   Mon, 1 Aug 2022 23:59:22 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, Rob Clark <robdclark@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 09/15] drm/gem: Add LRU/shrinker helper

On 8/1/22 23:42, Rob Clark wrote:
> On Mon, Aug 1, 2022 at 1:26 PM Dmitry Osipenko
> <dmitry.osipenko@...labora.com> wrote:
>>
>> On 8/1/22 23:13, Dmitry Osipenko wrote:
>>> On 8/1/22 23:11, Dmitry Osipenko wrote:
>>>> On 8/1/22 23:00, Rob Clark wrote:
>>>>> On Mon, Aug 1, 2022 at 12:41 PM Dmitry Osipenko
>>>>> <dmitry.osipenko@...labora.com> wrote:
>>>>>>
>>>>>> On 7/26/22 20:50, Rob Clark wrote:
>>>>>>> +/**
>>>>>>> + * drm_gem_lru_remove - remove object from whatever LRU it is in
>>>>>>> + *
>>>>>>> + * If the object is currently in any LRU, remove it.
>>>>>>> + *
>>>>>>> + * @obj: The GEM object to remove from current LRU
>>>>>>> + */
>>>>>>> +void
>>>>>>> +drm_gem_lru_remove(struct drm_gem_object *obj)
>>>>>>> +{
>>>>>>> +     struct drm_gem_lru *lru = obj->lru;
>>>>>>> +
>>>>>>> +     if (!lru)
>>>>>>> +             return;
>>>>>>> +
>>>>>>> +     mutex_lock(lru->lock);
>>>>>>> +     lru_remove(obj);
>>>>>>> +     mutex_unlock(lru->lock);
>>>>>>> +}
>>>>>>> +EXPORT_SYMBOL(drm_gem_lru_remove);
>>>>>>
>>>>>> I made a preliminary port of the DRM-SHMEM shrinker on top of the the
>>>>>> latest version of dma-buf locking convention and yours LRU patches. It
>>>>>> all works good, the only thing that is missing for the DRM-SHMEM
>>>>>> shrinker is the drm_gem_lru_remove_locked().
>>>>>>
>>>>>> What about to add a locked variant of drm_gem_lru_remove()?
>>>>>
>>>>> Sounds fine to me.. the only reason it didn't exist yet was because it
>>>>> wasn't needed yet..
>>>>
>>>> There is no use for the drm_gem_lru_move_tail_locked() as well, you're
>>>> not using it in the MSM driver. Hence I thought it might be good to add
>>>> the drm_gem_lru_remove_locked(), or maybe the
>>>> drm_gem_lru_move_tail_locked() should be dropped then?
>>>>
>>>>> I can respin w/ an addition of a _locked() version, or you can add it
>>>>> on top in your patchset.  Either is fine by me
>>>>
>>>> The either option is fine by me too. If you'll keep the unused
>>>> drm_gem_lru_move_tail_locked(), then will be nice to add
>>>> drm_gem_lru_remove_locked().
>>>>
>>>
>>> The drm_gem_lru_move_tail_locked() will be needed by DRM-SHMEM shrinker,
>>> BTW.
>>
>> On the other hand, I see now that DRM-SHMEM shrinker can use the
>> unlocked versions only. Hence both drm_gem_lru_move_tail_locked() and
>> drm_gem_lru_remove_locked() aren't needed.
> 
> drm_gem_lru_move_tail_locked() is used internally, but I guess it
> could be made static since there ended up not being external users
> (yet?)

Making it static will be good.

> I could see _move_tail_locked() being useful for a driver that wanted
> to bulk update a bunch of GEM objs, for ex. all the bo's associated
> with a submit/job.

At minimum we shouldn't expose the unused kernel symbols. But if you're
planning to make use of this function later on, then it might be fine to
add it.

-- 
Best regards,
Dmitry