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Subject: Re: [ATCH v3 0/4] Improve visibility of writeback
From: Kemeng Shi <shikemeng@huaweicloud.com>
To: akpm@linux-foundation.org, willy@infradead.org, jack@suse.cz,
 bfoster@redhat.com, tj@kernel.org
Cc: dsterba@suse.com, mjguzik@gmail.com, dhowells@redhat.com,
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 linux-fsdevel@vger.kernel.org
References: <20240422160539.3340-1-shikemeng@huaweicloud.com>
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Date: Mon, 22 Apr 2024 15:52:49 +0800
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on 4/23/2024 12:05 AM, Kemeng Shi wrote:
Forget to fix a build warning, please ignore this series. Sorry for the
noise.
> 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 no 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 (4):
>   writeback: collect stats of all wb of bdi in bdi_debug_stats_show
>   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              | 174 +++++++++++++++++++++++++++++-----
>  mm/page-writeback.c           |  27 +++++-
>  tools/writeback/wb_monitor.py | 172 +++++++++++++++++++++++++++++++++
>  4 files changed, 345 insertions(+), 29 deletions(-)
>  create mode 100644 tools/writeback/wb_monitor.py
>