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

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Date:   Thu, 12 Jan 2023 09:17:21 +0100
From:   Christian König <christian.koenig@....com>
To:     Shakeel Butt <shakeelb@...gle.com>,
        "T.J. Mercier" <tjmercier@...gle.com>
Cc:     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>,
        Todd Kjos <tkjos@...roid.com>,
        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>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>, android-mm@...gle.com,
        jstultz@...gle.com, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        daniel.vetter@...ll.ch
Subject: Re: [PATCH 0/4] Track exported dma-buffers with memcg

Am 12.01.23 um 09:13 schrieb Shakeel Butt:
> On Wed, Jan 11, 2023 at 04:49:36PM -0800, T.J. Mercier wrote:
> [...]
>>> 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?
>>>
>> I'm also not sure that we can depend on the dmabuf being backed at
>> export time 100% of the time? (They are for dmabuf heaps.) If not,
>> that'd make calling the existing memcg folio based functions a bit
>> difficult.
>>
> Where does the actual memory get allocated? I see the first patch is
> updating the stat in dma_buf_export() and dma_buf_release(). Does the
> memory get allocated and freed in those code paths?

Nope, dma_buf_export() just makes the memory available to others.

The driver which calls dma_buf_export() is the one allocating the memory.

Regards,
Christian.