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Subject: Re: [PATCH] bcache: make writeback_cutoff and writeback_cutoff_sync
 writeable
To:     Dongdong Tao <tdd21151186@gmail.com>
Cc:     dongdong.tao@canonical.com,
        Kent Overstreet <kent.overstreet@gmail.com>,
        "open list:BCACHE (BLOCK LAYER CACHE)" <linux-bcache@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
References: <20201105141939.9223-1-tdd21151186@gmail.com>
From:   Coly Li <colyli@suse.de>
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Message-ID: <14dd22de-030e-c7af-494b-a4317afeb795@suse.de>
Date:   Thu, 5 Nov 2020 22:23:12 +0800
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On 2020/11/5 22:19, Dongdong Tao wrote:
> From: dongdong tao <dongdong.tao@canonical.com>
> 
> commit 9aaf51654672 ("bcache: make cutoff_writeback and
> cutoff_writeback_sync tunable") intend to make these two option
> configurable by user, but these two are still read-only.
> 
> Signed-off-by: dongdong tao <dongdong.tao@canonical.com>
> ---
>  drivers/md/bcache/sysfs.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
> index 554e3afc9b68..81f4a681705c 100644
> --- a/drivers/md/bcache/sysfs.c
> +++ b/drivers/md/bcache/sysfs.c
> @@ -102,8 +102,8 @@ read_attribute(writeback_keys_done);
>  read_attribute(writeback_keys_failed);
>  read_attribute(io_errors);
>  read_attribute(congested);
> -read_attribute(cutoff_writeback);
> -read_attribute(cutoff_writeback_sync);
> +rw_attribute(cutoff_writeback);
> +rw_attribute(cutoff_writeback_sync);
>  rw_attribute(congested_read_threshold_us);
>  rw_attribute(congested_write_threshold_us);
>  
> @@ -902,6 +902,8 @@ STORE(__bch_cache_set)
>  	sysfs_strtoul_bool(copy_gc_enabled,	c->copy_gc_enabled);
>  	sysfs_strtoul_bool(idle_max_writeback_rate,
>  			   c->idle_max_writeback_rate_enabled);
> +	sysfs_strtoul_clamp(cutoff_writeback, bch_cutoff_writeback, 1, 100);
> +	sysfs_strtoul_clamp(cutoff_writeback_sync, bch_cutoff_writeback_sync, 1, 100);
>  

NACK, we only support the default value. Commit 9aaf51654672 ("bcache:
make cutoff_writeback and cutoff_writeback_sync tunable") clearly
announced the purpose was for research and experiment.

Coly Li