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From: Coly Li <colyli@suse.de>
To: "Norman.Kern" <norman.kern@gmx.com>
Cc: linux-block@vger.kernel.org, axboe@kernel.dk,
	linux-bcache@vger.kernel.org
Subject: Re: Large latency with bcache for Ceph OSD
Date: Fri, 26 Feb 2021 17:54:08 +0800	[thread overview]
Message-ID: <04770825-b1d2-8ec0-2345-77d49d99631a@suse.de> (raw)
In-Reply-To: <b808dde3-cb58-907b-4df0-e0eb2938b51e@gmx.com>

On 2/26/21 4:57 PM, Norman.Kern wrote:
>
[snipped]
>> You may try to trigger a gc by writing to
>> sys/fs/bcache/<cache-set-uuid>/internal/trigger_gc
>>
> When all cache had written back, I triggered gc, it recalled.
> 
> root@WXS0106:~# cat /sys/block/bcache0/bcache/cache/cache_available_percent
> 30
> 
> root@WXS0106:~# echo 1 > /sys/block/bcache0/bcache/cache/internal/trigger_gc
> root@WXS0106:~# cat /sys/block/bcache0/bcache/cache/cache_available_percent
> 97
> 
> Why must I trigger gc manually? Is not a default action of bcache-gc thread? And I found it can only work when all dirty data written back.
> 

1, GC is automatically triggered after some mount of data consumed. I
guess it is just not about time in your situation.

2, Because the gc will shrink all cached clean data, which is very
unfriendly for read-intend workload. Therefore gc_after_writeback is
defaulted as 0, when this sysfs file content set to 1, a gc will trigger
after the writeback accomplished.

Coly Li





  reply	other threads:[~2021-02-26  9:57 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-18  7:56 Large latency with bcache for Ceph OSD Norman.Kern
2021-02-21 23:48 ` Norman.Kern
2021-02-24  8:52   ` Coly Li
2021-02-25  2:22     ` Norman.Kern
2021-02-25  2:23     ` Norman.Kern
2021-02-25 13:00       ` Norman.Kern
2021-02-25 14:44         ` Coly Li
2021-02-26  8:57           ` Norman.Kern
2021-02-26  9:54             ` Coly Li [this message]
2021-03-02  2:03               ` Norman.Kern
2021-03-02  5:30               ` Norman.Kern

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