On Tue, May 25, 2021 at 11:37:13AM -0700, 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.
Procfs also uses the proc/<pid>/fdinfo/<fd> file to expose some information about DMA-BUF fds. However, the existing procfs interfaces can only provide information about the buffers for which processes hold fds or have the buffers mmapped into their address space. The sysfs interface also exposes attachment statistics for each buffer.
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 major improvements over v1:
- 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.
Signed-off-by: Hridya Valsaraju hridya@google.com Reported-by: kernel test robot lkp@intel.com
Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org