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: > 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@xxxxxxxxxx> > Reported-by: kernel test robot <lkp@xxxxxxxxx> > --- Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
