linux-kernel - Re: [PATCH 0/4] Track exported dma-buffers with memcg

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Date:   Thu, 12 Jan 2023 07:56:31 +0000
From:   Shakeel Butt <shakeelb@...gle.com>
To:     "T.J. Mercier" <tjmercier@...gle.com>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Arve Hjønnevåg" <arve@...roid.com>,
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        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <brauner@...nel.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        "Christian König" <christian.koenig@....com>,
        Michal Hocko <mhocko@...nel.org>,
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        Muchun Song <muchun.song@...ux.dev>,
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        James Morris <jmorris@...ei.org>,
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Subject: Re: [PATCH 0/4] Track exported dma-buffers with memcg

On Wed, Jan 11, 2023 at 11:56:45PM +0100, Daniel Vetter wrote:
> 
[...]
> I think eventually, at least for other "account gpu stuff in cgroups" use
> case we do want to actually charge the memory.
> 
> The problem is a bit that with gpu allocations reclaim is essentially "we
> pass the error to userspace and they get to sort the mess out". There are
> some exceptions (some gpu drivers to have shrinkers) would we need to make
> sure these shrinkers are tied into the cgroup stuff before we could enable
> charging for them?
> 

No, there is no requirement to have shrinkers or making such memory
reclaimable before charging it. Though existing shrinkers and the
possible future shrinkers would need to be converted into memcg aware
shrinkers.

Though there will be a need to update user expectations that if they 
use memcgs with hard limits, they may start seeing memcg OOMs after the
charging of dmabuf.

> Also note that at least from the gpu driver side this is all a huge
> endeavour, so if we can split up the steps as much as possible (and get
> something interim useable that doesn't break stuff ofc), that is
> practically need to make headway here. 

This sounds reasonable to me.