[0/4] Printbufs & shrinker OOM reporting

Message

Kent Overstreet April 19, 2022, 8:31 p.m. UTC

Debugging OOMs has been one of my sources of frustration, so this patch series
is an attempt to do something about it.

The first patch in the series is something I've been slowly evolving in bcachefs
for years: simple heap allocated strings meant for appending to and building up
structured log/error messages. They make it easy and straightforward to write
pretty-printers for everything, which in turn makes good logging and error
messages something that just happens naturally.

We want it here because that means the reporting I'm adding to shrinkers can be
used by both OOM reporting, and for the sysfs (or is it debugfs now) interface
that Roman is adding.

This patch series also:
 - adds OOM reporting on shrinkers, reporting on top 10 shrinkers (in sorted
   order!)
 - changes slab reporting to be always-on, also reporting top 10 slabs in sorted
   order
 - starts centralizing OOM reporting in mm/show_mem.c
 
The last patch in the series is only a demonstration of how to implement the
shrinker .to_text() method, since bcachefs isn't upstream yet.

Kent Overstreet (4):
  lib/printbuf: New data structure for heap-allocated strings
  mm: Add a .to_text() method for shrinkers
  mm: Centralize & improve oom reporting in show_mem.c
  bcachefs: shrinker.to_text() methods

 fs/bcachefs/btree_cache.c     |  18 ++-
 fs/bcachefs/btree_key_cache.c |  18 ++-
 include/linux/printbuf.h      | 140 ++++++++++++++++++
 include/linux/shrinker.h      |   5 +
 lib/Makefile                  |   4 +-
 lib/printbuf.c                | 271 ++++++++++++++++++++++++++++++++++
 mm/Makefile                   |   2 +-
 mm/oom_kill.c                 |  23 ---
 {lib => mm}/show_mem.c        |  14 ++
 mm/slab.h                     |   6 +-
 mm/slab_common.c              |  53 ++++++-
 mm/vmscan.c                   |  75 ++++++++++
 12 files changed, 587 insertions(+), 42 deletions(-)
 create mode 100644 include/linux/printbuf.h
 create mode 100644 lib/printbuf.c
 rename {lib => mm}/show_mem.c (78%)