[v4,0/6] mm: introduce shrinker debugfs interface

Message

Roman Gushchin May 25, 2022, 8:25 p.m. UTC

The only existing debugging mechanism is a couple of tracepoints in
do_shrink_slab(): mm_shrink_slab_start and mm_shrink_slab_end. They aren't
covering everything though: shrinkers which report 0 objects will never show up,
there is no support for memcg-aware shrinkers. Shrinkers are identified by their
scan function, which is not always enough (e.g. hard to guess which super
block's shrinker it is having only "super_cache_scan").

To provide a better visibility and debug options for memory shrinkers
this patchset introduces a /sys/kernel/debug/shrinker interface, to some extent
similar to /sys/kernel/slab.

For each shrinker registered in the system a directory is created.
As now, the directory will contain only a "scan" file, which allows to get
the number of managed objects for each memory cgroup (for memcg-aware shrinkers)
and each numa node (for numa-aware shrinkers on a numa machine). Other
interfaces might be added in the future.

To make debugging more pleasant, the patchset also names all shrinkers,
so that debugfs entries can have meaningful names.


v4:
  1) multiple shrinkers naming enhancements, by Kent and Dave
  2) multiple minor fixes/optimizations, by Muchun

v3:
  1) separated the "scan" part into a separate patch, by Dave
  2) merged *_memcg, *_node and *_memcg_node interfaces, by Dave
  3) shrinkers naming enhancements, by Christophe and Dave
  4) added signal_pending() check, by Hillf
  5) enabled by default, by Dave

v2:
  1) switched to debugfs, suggested by Mike, Andrew, Greg and others
  2) switched to seq_file API for output, no PAGE_SIZE limit anymore, by Andrew
  3) switched to down_read_killable(), suggested by Hillf
  4) dropped stateful filtering and "freed" returning, by Kent
  5) added docs, by Andrew
  6) added memcg_shrinker.py tool

rfc:
  https://lwn.net/Articles/891542/


Roman Gushchin (6):
  mm: memcontrol: introduce mem_cgroup_ino() and
    mem_cgroup_get_from_ino()
  mm: shrinkers: introduce debugfs interface for memory shrinkers
  mm: shrinkers: provide shrinkers with names
  mm: docs: document shrinker debugfs
  tools: add memcg_shrinker.py
  mm: shrinkers: add scan interface for shrinker debugfs

 Documentation/admin-guide/mm/index.rst        |   1 +
 .../admin-guide/mm/shrinker_debugfs.rst       | 131 ++++++++
 arch/x86/kvm/mmu/mmu.c                        |   2 +-
 drivers/android/binder_alloc.c                |   2 +-
 drivers/gpu/drm/i915/gem/i915_gem_shrinker.c  |   3 +-
 drivers/gpu/drm/msm/msm_gem_shrinker.c        |   2 +-
 .../gpu/drm/panfrost/panfrost_gem_shrinker.c  |   2 +-
 drivers/gpu/drm/ttm/ttm_pool.c                |   2 +-
 drivers/md/bcache/btree.c                     |   2 +-
 drivers/md/dm-bufio.c                         |   3 +-
 drivers/md/dm-zoned-metadata.c                |   4 +-
 drivers/md/raid5.c                            |   2 +-
 drivers/misc/vmw_balloon.c                    |   2 +-
 drivers/virtio/virtio_balloon.c               |   2 +-
 drivers/xen/xenbus/xenbus_probe_backend.c     |   2 +-
 fs/btrfs/super.c                              |   2 +
 fs/erofs/utils.c                              |   2 +-
 fs/ext4/extents_status.c                      |   3 +-
 fs/f2fs/super.c                               |   2 +-
 fs/gfs2/glock.c                               |   2 +-
 fs/gfs2/main.c                                |   2 +-
 fs/jbd2/journal.c                             |   3 +-
 fs/mbcache.c                                  |   2 +-
 fs/nfs/nfs42xattr.c                           |   7 +-
 fs/nfs/super.c                                |   2 +-
 fs/nfsd/filecache.c                           |   2 +-
 fs/nfsd/nfscache.c                            |   3 +-
 fs/quota/dquot.c                              |   2 +-
 fs/super.c                                    |   6 +-
 fs/ubifs/super.c                              |   2 +-
 fs/xfs/xfs_buf.c                              |   3 +-
 fs/xfs/xfs_icache.c                           |   2 +-
 fs/xfs/xfs_qm.c                               |   3 +-
 include/linux/memcontrol.h                    |  21 ++
 include/linux/shrinker.h                      |  31 +-
 kernel/rcu/tree.c                             |   2 +-
 lib/Kconfig.debug                             |   9 +
 mm/Makefile                                   |   1 +
 mm/huge_memory.c                              |   4 +-
 mm/memcontrol.c                               |  23 ++
 mm/shrinker_debug.c                           | 285 ++++++++++++++++++
 mm/vmscan.c                                   |  64 +++-
 mm/workingset.c                               |   2 +-
 mm/zsmalloc.c                                 |   3 +-
 net/sunrpc/auth.c                             |   2 +-
 tools/cgroup/memcg_shrinker.py                |  71 +++++
 46 files changed, 684 insertions(+), 46 deletions(-)
 create mode 100644 Documentation/admin-guide/mm/shrinker_debugfs.rst
 create mode 100644 mm/shrinker_debug.c
 create mode 100755 tools/cgroup/memcg_shrinker.py