linux-kernel - Re: [PATCH v1 0/5] Add memory shrinker to VirtIO-GPU DRM driver

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Date:   Thu, 10 Mar 2022 20:02:22 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        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>,
        Gert Wollny <gert.wollny@...labora.com>
Cc:     Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        dri-devel@...ts.freedesktop.org, Dmitry Osipenko <digetx@...il.com>
Subject: Re: [PATCH v1 0/5] Add memory shrinker to VirtIO-GPU DRM driver

Hi

Am 09.03.22 um 23:25 schrieb Dmitry Osipenko:
>>
>> The reason for this work is to keep GEM shmem pages mapped and allocated
>> even while the BO is neither mapped nor pinned.  As it is now, GEM SHMEM
>> creates and releases pages on each pin and unpin, and maps and unmaps
>> memory ranges on each vmap and vunmap.  It's all wasteful. Only the
>> first pin and vmap calls should establish pages and mappings and only
>> the purge and free functions should release them.
> 
> Hm, aren't maps and pins already refcounted?

They are. But even when the refcounter reaches 0 on deref, there's no 
need to remove the mapping or free the memory pages. We can keep them 
around for the next ref operation.  Only the shrinker's purge or freeing 
the object has to do such clean-up operations.  Such behavior is 
supported by TTM and we already use it in VRAM helpers as well.

Best regards
Thomas

> 
>> The patchset adds new helpers for BO purging to struct
>> drm_gem_object_funcs. With this, I think it might be possible to have
>> one global DRM shrinker and let it handle all BOs; independent of each
>> BO's memory manager.
> 
> Thank you, I'll give it a try.

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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