blktrace: output cgroup info

From: Shaohua Li <[email protected]>

Hi,

Currently blktrace isn't cgroup aware. blktrace prints out task name of current context, but the task of current context isn't always in the cgroup where the BIO comes from. We can't use task name to find out IO cgroup. For example, Writeback BIOs always comes from flusher thread but the BIOs are for different blk cgroups. Request could be requeued and dispatched from completely different tasks. MD/DM are another examples. This brings challenges if we want to use blktrace for performance tunning with cgroup enabled.

This patchset try to fix the gap. We print out cgroup fhandle info in blktrace. Userspace can use open_by_handle_at() syscall to find the cgroup by fhandle. Or userspace can use name_to_handle_at() syscall to find fhandle for a cgroup and use a BPF program to filter out blktrace for a specific cgroup.

The first 6 patches adds export operation handlers for kernfs, so userspace can use open_by_handle_at/name_to_handle_at to a kernfs file. Later patches make blktrace output cgroup info.

Thanks,
Shaohua

V4 -> V5:
- Add ack and refresh to latest -next

V3 -> V4:
- Address some issues pointed out by Tejun
- Fix build errors with latest -next tree

V2 -> V3:
- Uses 32 bits inode number
- Refresh to latest -next tree

V1 -> V2:
- Fix a bug in cgroup association
- Fix build errors reported by 0day
- Address some issues pointed out by Tejun

Shaohua Li (11):
kernfs: use idr instead of ida to manage inode number
kernfs: implement i_generation
kernfs: add an API to get kernfs node from inode number
kernfs: don't set dentry->d_fsdata
kernfs: introduce kernfs_node_id
kernfs: add exportfs operations
cgroup: export fhandle info for a cgroup
blktrace: export cgroup info in trace
block: always attach cgroup info into bio
blktrace: add an option to allow displaying cgroup path
block: use standard blktrace API to output cgroup info for debug notes

 block/bfq-iosched.h               |  13 +-
 block/blk-throttle.c              |  13 +-
 block/cfq-iosched.c               |  15 +--
 fs/kernfs/dir.c                   | 111 ++++++++++++----
 fs/kernfs/file.c                  |  10 +-
 fs/kernfs/inode.c                 |   9 +-
 fs/kernfs/kernfs-internal.h       |   9 ++
 fs/kernfs/mount.c                 |  94 ++++++++++++--
 fs/kernfs/symlink.c               |   6 +-
 include/linux/blk-cgroup.h        |   3 +
 include/linux/blktrace_api.h      |  13 +-
 include/linux/cgroup.h            |  16 ++-
 include/linux/kernfs.h            |  28 ++++-
 include/trace/events/writeback.h  |   2 +-
 include/uapi/linux/blktrace_api.h |   3 +
 kernel/cgroup/cgroup.c            |  15 ++-
 kernel/trace/blktrace.c           | 259 ++++++++++++++++++++++++++------------
 17 files changed, 467 insertions(+), 152 deletions(-)

2.9.3