Re: [RFC v2 6/6] android: binder: Add a buffer flag to relinquish ownership of fds

From: John Stultz <john.stultz@linaro.org>
To: Todd Kjos <tkjos@google.com>
Cc: "Zefan Li" <lizefan.x@bytedance.com>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	"David Airlie" <airlied@linux.ie>,
	"DRI mailing list" <dri-devel@lists.freedesktop.org>,
	"Benjamin Gaignard" <benjamin.gaignard@linaro.org>,
	"Kalesh Singh" <kaleshsingh@google.com>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	Kenny.Ho@amd.com, "Jonathan Corbet" <corbet@lwn.net>,
	"Suren Baghdasaryan" <surenb@google.com>,
	"Laura Abbott" <labbott@redhat.com>,
	linux-media <linux-media@vger.kernel.org>,
	"Todd Kjos" <tkjos@android.com>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"moderated list:DMA BUFFER SHARING FRAMEWORK"
	<linaro-mm-sig@lists.linaro.org>, "Tejun Heo" <tj@kernel.org>,
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	"Martijn Coenen" <maco@android.com>,
	"T.J. Mercier" <tjmercier@google.com>,
	"Christian Brauner" <brauner@kernel.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Liam Mark" <lmark@codeaurora.org>,
	"Christian König" <christian.koenig@amd.com>,
	"Arve Hjønnevåg" <arve@android.com>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Hridya Valsaraju" <hridya@google.com>
Subject: Re: [RFC v2 6/6] android: binder: Add a buffer flag to relinquish ownership of fds
Date: Mon, 14 Feb 2022 12:37:11 -0800	[thread overview]
Message-ID: <CALAqxLVeLsv9ESCL2EoZQ8-tRgp0V+tmdYbkyakFetf=ewTH+A@mail.gmail.com> (raw)
In-Reply-To: <CAHRSSEzsn-EVKXTRfmpbPR9u0wNpdvdZoX64Tm_mB1DQMRSUPQ@mail.gmail.com>

On Mon, Feb 14, 2022 at 12:19 PM Todd Kjos <tkjos@google.com> wrote:
> On Mon, Feb 14, 2022 at 11:29 AM Suren Baghdasaryan <surenb@google.com> wrote:
> > On Mon, Feb 14, 2022 at 10:33 AM Todd Kjos <tkjos@google.com> wrote:
> > >
> > > Since we are creating a new gpu cgroup abstraction, couldn't this
> > > "transfer" be done in userspace by the target instead of in the kernel
> > > driver? Then this patch would reduce to just a flag on the buffer
> > > object.
> >
> > Are you suggesting to have a userspace accessible cgroup interface for
> > transferring buffer charges and the target process to use that
> > interface for requesting the buffer to be charged to its cgroup?
>
> Well, I'm asking why we need to do these cgroup-ish actions in the
> kernel when it seems more natural to do it in userspace.
>

In case its useful, some additional context from some of the Linux
Plumber's discussions last fall:

Daniel Stone outlines some concerns with the cgroup userland handling
for accounting:
  https://youtu.be/3OqllZONTiQ?t=3430

And the binder ownership transfer bit was suggested here by Daniel Vetter:
  https://youtu.be/3OqllZONTiQ?t=3730

thanks
-john