| Message ID | 20190322025135.118201-1-fengc@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Improve the dma-buf tracking | expand |
On Thu, Mar 21, 2019 at 07:51:32PM -0700, Chenbo Feng 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 count, > 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 are > 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, calling > stat(2) on each entry gives the caller a unique ID (st_ino), the buffer's > size (st_size), and even the number of pages assigned to each dma-buffer. > Secoundly, add the inode information to /sys/kernel/debug/dma_buf/bufinfo > so in the case where a buffer is mmap()ed into a process’s address space Is there a better place to add bufinfo than debugfs, since debugfs is not something Android may mount for non-debug uses in the future? > 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-bufs > which lets userspace assign short names (e.g., "CAMERA") to buffers. This > information can be extremely helpful for tracking and accounting shared > 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() handler > to dma_buf_file_operations. The handler will print the file_count and name > of each buffer. There are a couple more entries shown in fdinfo per patch 3/3 so it is worth mentioning those here as well. Also, is there kselftests to add or modify? I suggest we add those since they are always invaluable. I'll review more soon. Currently traveling. I am especially curious how you created the new inodes since I recently had to do so for another usecase as well. thanks! - Joel > > Change in v2: > * Add a check to prevent changing dma-buf name when it is attached to > devices. > * Fixed some compile warnings > > 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 > > 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 >
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 count, 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 are 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, calling stat(2) on each entry gives the caller a unique ID (st_ino), the buffer's size (st_size), and even the number of pages assigned to each dma-buffer. Secoundly, add the inode information to /sys/kernel/debug/dma_buf/bufinfo so in the case where a buffer is mmap()ed into a process’s address 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-bufs which lets userspace assign short names (e.g., "CAMERA") to buffers. This information can be extremely helpful for tracking and accounting shared 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() handler to dma_buf_file_operations. The handler will print the file_count and name of each buffer. Change in v2: * Add a check to prevent changing dma-buf name when it is attached to devices. * Fixed some compile warnings 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 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(-)