linux-kernel - Re: [PATCH 0/6] Improve visibility of writeback

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Message-ID: <20240320172240.7buswiv7zj2m5odg@quack3>
Date: Wed, 20 Mar 2024 18:22:40 +0100
From: Jan Kara <jack@...e.cz>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: akpm@...ux-foundation.org, tj@...nel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	willy@...radead.org, bfoster@...hat.com, jack@...e.cz,
	dsterba@...e.com, mjguzik@...il.com, dhowells@...hat.com,
	peterz@...radead.org
Subject: Re: [PATCH 0/6] Improve visibility of writeback

On Wed 20-03-24 19:02:16, Kemeng Shi wrote:
> 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 4 add wb_monitor.py to monitor basic writeback info
> of running system, more info could be added on demand. Rest patches
> are some random cleanups. 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 /sys/kernel/debug/bdi/252:16/stats:
> BdiWriteback:              448 kB
> BdiReclaimable:        1303904 kB
> BdiDirtyThresh:      189914124 kB
> DirtyThresh:         195337564 kB
> BackgroundThresh:     32516508 kB
> BdiDirtied:            3591392 kB
> BdiWritten:            2287488 kB
> BdiWriteBandwidth:      322248 kBps
> b_dirty:                     0
> b_io:                        0
> b_more_io:                   2
> b_dirty_time:                0
> bdi_list:                    1
> state:                       1
> 
> /* per wb writeback info is collected */
> # cat /sys/kernel/debug/bdi/252:16/wb_stats:
> cat 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:                 4284
> WbWriteback:              448 kB
> WbReclaimable:         818944 kB
> WbDirtyThresh:        3096524 kB
> WbDirtied:            2266880 kB
> WbWritten:            1447936 kB
> WbWriteBandwidth:      214036 kBps
> b_dirty:                    0
> b_io:                       0
> b_more_io:                  1
> b_dirty_time:               0
> state:                      5
> WbCgIno:                 4325
> WbWriteback:              224 kB
> WbReclaimable:         819392 kB
> WbDirtyThresh:        2920088 kB
> WbDirtied:            2551808 kB
> WbWritten:            1732416 kB
> WbWriteBandwidth:      201832 kBps
> b_dirty:                    0
> b_io:                       0
> b_more_io:                  1
> b_dirty_time:               0
> state:                      5
> 
> /* monitor writeback info */
> # ./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
> ...

So I'm wondering: Are you implementing this just because this looks
interesting or do you have a real need for the functionality? Why?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR