Re: [PATCH v3] dmabuf: Add the capability to expose DMA-BUF stats in sysfs

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jan 26, 2021 at 12:42:36PM -0800, Hridya Valsaraju wrote:
> This patch allows statistics to be enabled for each DMA-BUF in
> sysfs by enabling the config CONFIG_DMABUF_SYSFS_STATS.
> 
> The following stats will be exposed by the interface:
> 
> /sys/kernel/dmabuf/buffers/<inode_number>/exporter_name
> /sys/kernel/dmabuf/buffers/<inode_number>/size
> /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/device
> /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter
> 
> The inode_number is unique for each DMA-BUF and was added earlier [1]
> in order to allow userspace to track DMA-BUF usage across different
> processes.
> 
> Currently, this information is exposed in
> /sys/kernel/debug/dma_buf/bufinfo.
> However, since debugfs is considered unsafe to be mounted in production,
> it is being duplicated in sysfs.
> 
> This information will be used to derive DMA-BUF
> per-exporter stats and per-device usage stats for Android Bug reports.
> The corresponding userspace changes can be found at [2].
> Telemetry tools will also capture this information(along with other
> memory metrics) periodically as well as on important events like a
> foreground app kill (which might have been triggered by Low Memory
> Killer). It will also contribute to provide a snapshot of the system
> memory usage on other events such as OOM kills and Application Not
> Responding events.
> 
> A shell script that can be run on a classic Linux environment to read
> out the DMA-BUF statistics can be found at [3](suggested by John
> Stultz).
> 
> The patch contains the following improvements over the previous version:
> 1) Each attachment is represented by its own directory to allow creating
> a symlink to the importing device and to also provide room for future
> expansion.
> 2) The number of distinct mappings of each attachment is exposed in a
> separate file.
> 3) The per-buffer statistics are now in /sys/kernel/dmabuf/buffers
> inorder to make the interface expandable in future.
> 
> All of the improvements above are based on suggestions/feedback from
> Daniel Vetter and Christian König.
> 
> [1]: https://lore.kernel.org/patchwork/patch/1088791/
> [2]: https://android-review.googlesource.com/q/topic:%22dmabuf-sysfs%22+(status:open%20OR%20status:merged)
> [3]: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/1549734
> 
> Signed-off-by: Hridya Valsaraju <hridya@google.com>
> Reported-by: kernel test robot <lkp@intel.com>
> ---
> Changes in v3:
> Fix a warning reported by the kernel test robot.
> 
> Changes in v2:
> -Move statistics to /sys/kernel/dmabuf/buffers in oder to allow addition
> of other DMA-BUF-related sysfs stats in future. Based on feedback from
> Daniel Vetter.
> -Each attachment has its own directory to represent attaching devices as
> symlinks and to introduce map_count as a separate file. Based on
> feedback from Daniel Vetter and Christian König. Thank you both!
> -Commit messages updated to point to userspace code in AOSP that will
> read the DMA-BUF sysfs stats.
> 
> 
>  .../ABI/testing/sysfs-kernel-dmabuf-buffers   |  52 ++++
>  drivers/dma-buf/Kconfig                       |  11 +
>  drivers/dma-buf/Makefile                      |   1 +
>  drivers/dma-buf/dma-buf-sysfs-stats.c         | 285 ++++++++++++++++++
>  drivers/dma-buf/dma-buf-sysfs-stats.h         |  62 ++++
>  drivers/dma-buf/dma-buf.c                     |  37 +++
>  include/linux/dma-buf.h                       |  20 ++
>  7 files changed, 468 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
>  create mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.c
>  create mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.h

I don't know the dma-buf code at all, but from a sysfs/kobject point of
view, this patch looks good to me:

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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