[PATCH v5 0/5] Improve visibility of writeback

[Kemeng Shi]

v4->v5:
-Add new patch to fix build problem of "writeback: support retrieving
per group debug writeback stats of bdi". The new fix patch can be folded
into it's pre-patch if the pre-patch is not merge into tree or it could
be pick-up to apply.

v3->v4:
-Fix build warning that filepages, headroom and writeback in
cgwb_calc_thresh is used uninitialized when CONFIG_CGROUP_WRITEBACK
is not enabled.

v2->v3:
-Drop patches to protect non-exist race and to define GDTC_INIT_NO_WB to
null.
-Add wb_tryget to wb from which we collect stats to bdi stats.
-Create wb_stats when CONFIG_CGROUP_WRITEBACK is not enabled.
-Add a blank line between two wb stats in wb_stats.

v1->v2:
-Send cleanup to wq_monitor.py separately.
-Add patch to avoid use after free of bdi.
-Rename wb_calc_cg_thresh to cgwb_calc_thresh as Tejun suggested.
-Use rcu walk to avoid use after free.
-Add debug output to each related patches.

This series tries to improve visilibity of writeback. Patch 1 make
/sys/kernel/debug/bdi/xxx/stats show writeback info of whole bdi
instead of only writeback info in root cgroup. Patch 2 add a new
debug file /sys/kernel/debug/bdi/xxx/wb_stats to show per wb writeback
info. Patch 3 add wb_monitor.py to monitor basic writeback info
of running system, more info could be added on demand. Patch 4
is a random cleanup. More details can be found in respective
patches. Thanks!

Following domain hierarchy is tested:
                global domain (320G)
                /                 \
        cgroup domain1(10G)     cgroup domain2(10G)
                |                 |
bdi            wb1               wb2

/* all writeback info of bdi is successfully collected */
cat stats
BdiWriteback:             4704 kB
BdiReclaimable:        1294496 kB
BdiDirtyThresh:      204208088 kB
DirtyThresh:         195259944 kB
BackgroundThresh:     32503588 kB
BdiDirtied:           48519296 kB
BdiWritten:           47225696 kB
BdiWriteBandwidth:     1173892 kBps
b_dirty:                     1
b_io:                        0
b_more_io:                   1
b_dirty_time:                0
bdi_list:                    1
state:                       1

/* per wb writeback info of bdi is collected */
cat /sys/kernel/debug/bdi/252:16/wb_stats
WbCgIno:                    1
WbWriteback:                0 kB
WbReclaimable:              0 kB
WbDirtyThresh:              0 kB
WbDirtied:                  0 kB
WbWritten:                  0 kB
WbWriteBandwidth:      102400 kBps
b_dirty:                    0
b_io:                       0
b_more_io:                  0
b_dirty_time:               0
state:                      1

WbCgIno:                 4208
WbWriteback:            59808 kB
WbReclaimable:         676480 kB
WbDirtyThresh:        6004624 kB
WbDirtied:           23348192 kB
WbWritten:           22614592 kB
WbWriteBandwidth:      593204 kBps
b_dirty:                    1
b_io:                       1
b_more_io:                  0
b_dirty_time:               0
state:                      7

WbCgIno:                 4249
WbWriteback:           144256 kB
WbReclaimable:         432096 kB
WbDirtyThresh:        6004344 kB
WbDirtied:           25727744 kB
WbWritten:           25154752 kB
WbWriteBandwidth:      577904 kBps
b_dirty:                    0
b_io:                       1
b_more_io:                  0
b_dirty_time:               0
state:                      7

The wb_monitor.py script output is as following:
/wb_monitor.py 252:16 -c
                  writeback  reclaimable   dirtied   written    avg_bw
252:16_1                  0            0         0         0    102400
252:16_4284             672       820064   9230368   8410304    685612
252:16_4325             896       819840  10491264   9671648    652348
252:16                 1568      1639904  19721632  18081952   1440360

                  writeback  reclaimable   dirtied   written    avg_bw
252:16_1                  0            0         0         0    102400
252:16_4284             672       820064   9230368   8410304    685612
252:16_4325             896       819840  10491264   9671648    652348
252:16                 1568      1639904  19721632  18081952   1440360
..


Kemeng Shi (5):
  writeback: collect stats of all wb of bdi in bdi_debug_stats_show
  writeback: support retrieving per group debug writeback stats of bdi
  writeback: fix build problems of "writeback: support retrieving per
    group debug writeback stats of bdi"
  writeback: add wb_monitor.py script to monitor writeback info on bdi
  writeback: rename nr_reclaimable to nr_dirty in balance_dirty_pages

 include/linux/writeback.h     |   1 +
 mm/backing-dev.c              | 177 +++++++++++++++++++++++++++++-----
 mm/page-writeback.c           |  27 +++++-
 tools/writeback/wb_monitor.py | 172 +++++++++++++++++++++++++++++++++
 4 files changed, 348 insertions(+), 29 deletions(-)
 create mode 100644 tools/writeback/wb_monitor.py

-- 
2.30.0