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

On 17/11/17 10:20, Rui Hua wrote:

Hi, Stefan

2017-11-17 16:28 GMT+08:00 Stefan Priebe - Profihost AG [off-list ref]:

quoted

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.

regards,
Eddie