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From:   Sumit Semwal <sumit.semwal@linaro.org>
Date:   Mon, 18 Mar 2019 21:47:12 +0530
Message-ID: <CAO_48GEFz99yL34NSB5TCrg1S0X00Z_UysoFugozGK3aEazGig@mail.gmail.com>
Subject: Re: [RFC dma-buf 0/3] Improve the dma-buf tracking
To:     Daniel Vetter <daniel@ffwll.ch>
Cc:     Chenbo Feng <fengc@google.com>, erickreyes@google.com,
        LKML <linux-kernel@vger.kernel.org>,
        DRI mailing list <dri-devel@lists.freedesktop.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@vger.kernel.org>
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Hi Daniel,

On Fri, 15 Mar 2019 at 16:36, Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Thu, Mar 14, 2019 at 6:49 PM Sumit Semwal <sumit.semwal@linaro.org> wr=
ote:
> >
> > Hello Chenbo,Thank you for your RFC series.
> >
> > On Wed, 27 Feb 2019 at 09:24, Chenbo Feng <fengc@google.com> wrote:
> > >
> > > Currently, all dma-bufs share the same anonymous inode. While we can =
count
> > > how many dma-buf fds or mappings a process has, we can't get the size=
 of
> > > the backing buffers or tell if two entries point to the same dma-buf.=
 And
> > > in debugfs, we can get a per-buffer breakdown of size and reference c=
ount,
> > > but can't tell which processes are actually holding the references to=
 each
> > > buffer.
> > >
> > > To resolve the issue above and provide better method for userspace to=
 track
> > > the dma-buf usage across different processes, the following changes a=
re
> > > proposed in dma-buf kernel side. First of all, replace the singleton =
inode
> > > inside the dma-buf subsystem with a mini-filesystem, and assign each
> > > dma-buf a unique inode out of this filesystem.  With this change, cal=
ling
> > > stat(2) on each entry gives the caller a unique ID (st_ino), the buff=
er's
> > > size (st_size), and even the number of pages assigned to each dma-buf=
fer.
> > > Secoundly, add the inode information to /sys/kernel/debug/dma_buf/buf=
info
> > > so in the case where a buffer is mmap()ed into a process=E2=80=99s ad=
dress space
> > > but all remaining fds have been closed, we can still get the dma-buf
> > > information and try to accociate it with the process by searching the
> > > proc/pid/maps and looking for the corresponding inode number exposed =
in
> > > dma-buf debug fs. Thirdly, created an ioctl to assign names to dma-bu=
fs
> > > which lets userspace assign short names (e.g., "CAMERA") to buffers. =
This
> > > information can be extremely helpful for tracking and accounting shar=
ed
> > > buffers based on their usage and original purpose. Last but not least=
, add
> > > dma-buf information to /proc/pid/fdinfo by adding a show_fdinfo() han=
dler
> > > to dma_buf_file_operations. The handler will print the file_count and=
 name
> > > of each buffer.
> >
> > In general, I think I like the idea as it contributes to a much more
> > relevant usage analysis of dma-buf backed buffers.
> > I will get to doing a more detailed review soon, but immediately, we
> > might want to think a bit about the get/set_name IOCTLS - do we need
> > to think of disallowing multiple renaming of buffers once they start
> > getting used? It could otherwise make the whole metrics a lot
> > confused?
> >
> > >
> > > Greg Hackmann (3):
> > >   dma-buf: give each buffer a full-fledged inode
> > >   dma-buf: add DMA_BUF_{GET,SET}_NAME ioctls
> > >   dma-buf: add show_fdinfo handler
>
> I'm not seeing the patches, so just quick comment here: Some drivers
> (at least vc4) already have the concept of buffer names. Would be neat
> to integrate this between dma-buf and drm_gem in prime.
>
FYI, here's the patch series - https://patchwork.freedesktop.org/series/572=
82/

Best,
Sumit.

> Aside from that sounds like a good idea overall, but I can't see any deta=
ils.
> -Daniel
>
> > >
> > >  drivers/dma-buf/dma-buf.c    | 121 ++++++++++++++++++++++++++++++++-=
--
> > >  include/linux/dma-buf.h      |   5 +-
> > >  include/uapi/linux/dma-buf.h |   4 ++
> > >  include/uapi/linux/magic.h   |   1 +
> > >  4 files changed, 122 insertions(+), 9 deletions(-)
> > >
> > > --
> > > 2.21.0.rc2.261.ga7da99ff1b-goog
> > >
> >
> > Best,
> > Sumit.
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch


--=20
Thanks and regards,

Sumit Semwal
Linaro Consumer Group - Kernel Team Lead
Linaro.org =E2=94=82 Open source software for ARM SoCs