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List:       linux-bcache
Subject:    Re: journal replay at each boot problematic?
From:       Kai Krakow <hurikhan77 () gmail ! com>
Date:       2017-03-29 17:59:51
Message-ID: 20170329195951.604ad133 () jupiter ! sol ! kaishome ! de
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Am Wed, 29 Mar 2017 19:52:57 +0200
schrieb Kai Krakow <hurikhan77@gmail.com>:

> Am Wed, 29 Mar 2017 14:27:11 +0200
> schrieb Clemens Eisserer <linuxhippy@gmail.com>:
> 
> > Hi Kai,
> >   
> > > As far as the docs tell, bcache is designed to shut down unclean.
> > > So this is expected behavior in write-back mode.    
> > 
> > Yes, I also read it - but since I got a few btrfs fs errors when
> > running btrfs check (mostly space-cache related) I became a bit
> > alarmed.
> > As all csums are ok, so I don't think the backing/caching devices
> > are corrupt in any way.  
> 
> This is probably related to btrfs not closed properly or some bug in
> an older kernel. Space cache problems can usually be safely ignored as
> long as the kernel detects them. But maybe ask about this in the btrfs
> list. I'm pretty sure that is related to your shutdown procedure and
> not to bcache. I don't see such messages here without special
> workarounds in the shutdown procedure, however, I'm using initramfs
> created by dracut. It properly unmounts btrfs.
> 
> > > To cleanly detach a bcache, you would need to first put it in
> > > write-through or write-around mode and wait for write-back to
> > > finish. In turn, this mode should also avoid these messages at
> > > boot.    
> > 
> > This is exactly what I do now before each shutdown: switch to
> > writethrough and wait in a bash-loop until state="clean" -
> > sorrounded by two calls to sync.  
> 
> I don't think this is necessary. Just ensure that the FS is umounted
> or at least RO mounted, sync, and ensure that all storage buffers are
> flushed (SCSI, SATA, whatever). Btrfs may lazily still write data even
> in the RO mounted mode. This may be your problem. Bcache may even
> prevent further evil here because of its always-unclean writeback
> behavior.

Addendum: Maybe try "btrfs sync"...

> > However, I still get the journal replay messages at bootup:
> > 
> > [    2.590615] bcache: bch_journal_replay() journal replay done, 827
> > keys in 37 entries, seq 145717  
> 
> Do you properly close the FS before shutting down, i.e. unmount (and
> not only remount RO), and flush the storage layer?
> 



-- 
Regards,
Kai

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