Re: [PATCH] bcache: recover data from backing device when read request hit clean

From: Coly Li <colyli@suse.de>
To: Eddie Chapman <eddie@ehuk.net>
Cc: Rui Hua <huarui.dev@gmail.com>,
	Stefan Priebe - Profihost AG <s.priebe@profihost.ag>,
	Coly Li <i@coly.li>, Michael Lyle <mlyle@lyle.org>,
	Kent Overstreet <kent.overstreet@gmail.com>,
	linux-bcache@vger.kernel.org, linux-block@vger.kernel.org
Subject: Re: [PATCH] bcache: recover data from backing device when read request hit clean
Date: Fri, 17 Nov 2017 21:22:05 +0800	[thread overview]
Message-ID: <dc4a100c-e1c0-ff9b-4a13-a90faf8a9d06@suse.de> (raw)
In-Reply-To: <54dbc609-b448-68f6-bd9a-676fd5d21151@ehuk.net>

On 17/11/2017 8:57 PM, Eddie Chapman wrote:
> On 17/11/17 10:20, Rui Hua wrote:
>> Hi, Stefan
>>
>> 2017-11-17 16:28 GMT+08:00 Stefan Priebe - Profihost AG
>> <s.priebe@profihost.ag>:
>>> I‘m getting the same xfs error message under high load. Does this
>>> patch fix
>>> it?
>>>
>> Did you applied the patch "bcache: only permit to recovery read error
>> when cache device is clean" ?
>> If you did, maybe this patch can fix it. And you'd better check
>> /sys/fs/bcache/XXX/internal/cache_read_races in your environment,
>> meanwhile, it should not be zero when you get that err message.
> 
> Hi all,
> 
> I have 3 servers running a very recent 4.9 stable release, with several
> recent bcache patches cherry picked, including V4 of "bcache: only
> permit to recovery read error when cache device is clean".
> 
> In the 3 weeks since using these cherry picks I've experienced a very
> small number of isolated read errors in the layer above bcache, on all 3
> servers.
> 
> On one of the servers, 2 out of the 6 bcache resources have a value of 1
> in /sys/fs/bcache/XXX/internal/cache_read_races, and it is on these same
> 2 bcache resources where one read error has occurred on the upper layer.
> The other 4 bcache resources have 0 in cache_read_races and I haven't
> had any read errors on the layers above them.
> 
> On another server, I have 1 bcache resource out of 10 with a value of 5
> in /sys/fs/bcache/XXX/internal/cache_read_races, and it is on that
> bcache resource where a read error occurred on one occasion. The other 9
> bcache resources have 0 in cache_read_races, and no read errors have
> occurred on the layers above any of them.
> 
> On the 3rd server where some read errors occurred, I cannot verify if
> there were positive values in cache_read_races as I moved the data from
> there onto other storage, and shut down the bcache resources where the
> errors occurred.
> 
> If I can provide any other info which might help with this issue, please
> let me know.

Hi Eddie,

This is very informative, thank you so much :-)

Coly Li