linux-kernel - Re: [PATCH v4 1/4] writeback: collect stats of all wb of bdi in bdi_debug_stats

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Date: Mon, 22 Apr 2024 08:23:19 -1000
From: Tejun Heo <tj@...nel.org>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: akpm@...ux-foundation.org, willy@...radead.org, jack@...e.cz,
	bfoster@...hat.com, dsterba@...e.com, mjguzik@...il.com,
	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4 1/4] writeback: collect stats of all wb of bdi in
 bdi_debug_stats_show

On Tue, Apr 23, 2024 at 12:48:05AM +0800, Kemeng Shi wrote:
> /sys/kernel/debug/bdi/xxx/stats is supposed to show writeback information
> of whole bdi, but only writeback information of bdi in root cgroup is
> collected. So writeback information in non-root cgroup are missing now.
> To be more specific, considering following case:
> 
> /* create writeback cgroup */
> cd /sys/fs/cgroup
> echo "+memory +io" > cgroup.subtree_control
> mkdir group1
> cd group1
> echo $$ > cgroup.procs
> /* do writeback in cgroup */
> fio -name test -filename=/dev/vdb ...
> /* get writeback info of bdi */
> cat /sys/kernel/debug/bdi/xxx/stats
> The cat result unexpectedly implies that there is no writeback on target
> bdi.
> 
> Fix this by collecting stats of all wb in bdi instead of only wb in
> root cgroup.
> 
> 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:             2912 kB
> BdiReclaimable:        1598464 kB
> BdiDirtyThresh:      167479028 kB
> DirtyThresh:         195038532 kB
> BackgroundThresh:     32466728 kB
> BdiDirtied:           19141696 kB
> BdiWritten:           17543456 kB
> BdiWriteBandwidth:     1136172 kBps
> b_dirty:                     2
> b_io:                        0
> b_more_io:                   1
> b_dirty_time:                0
> bdi_list:                    1
> state:                       1
> 
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun