Re: [PATCH] nilfs-utils: Work around uncleanable full filesystem

[Vyacheslav Dubeyko <slava-yeENwD64cLxBDgjK7y7TUQ@public.gmane.org>]

On Mon, 2013-01-14 at 16:54 +0100, Sven Eckelmann wrote:
> The filesystem can end up in a state were the filesystem is full and the
> returned ss_nongc_ctime is smaller than sui_lastmod of all reclaimable
> segments. The garbage collector will not clean anything and therefore no new
> room for new files will be available and ss_nongc_ctime/sui_lastmod will not be
> updated without using special tools. This makes the filesystem unusable without
> manual recovery.
> 
> Signed-off-by: Sven Eckelmann <sven-KaDOiPu9UxWEi8DpZVb4nw@public.gmane.org>
> --
> This problem appeared on a current 3.2 stable kernel (Debian Wheezy build). I
> am not an FS developer and have therefore not much background knowledge about
> the NILFS codebase. Nevertheless, this problem hit me quite hard after creating
> some files on a nilfs partition until it was full and deleting them again.
> 
> $ for i in `seq 0 150`; do dd if=/dev/zero of=foo$i count=22528; done
> $ rm foo*
> 
> Looking at the output debugging output using
> 
> $ watch -n .5 'df -h;tail /var/log/syslog;'
> 
> clearly showed that it was not finding any segments to delete. The only problem
> I could find was the threshold. After "removing" this threshold, I was able to
> get some clear segments again. I personally cannot explain why the check is
> there at all. Maybe there is a good reason but the comment above it didn't help
> much.
> 
> So, here for completeness the threshold: 1358164666 (aka: Mon Jan 14 12:57:46
> CET 2013)
> 
> And here are the output of lssu and lscp:
> 
> $ lssu --all
> SEGNUM        DATE     TIME STAT     NBLOCKS
> 0  2013-01-14 12:58:23  -d-        2047
> 1  2013-01-14 12:58:23  -d-        2048

[snip]

> 
> Signed-off-by: Sven Eckelmann <sven-KaDOiPu9UxWEi8DpZVb4nw@public.gmane.org>
> ---
>  sbin/cleanerd/cleanerd.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sbin/cleanerd/cleanerd.c b/sbin/cleanerd/cleanerd.c
> index bfcd893..12ed975 100644
> --- a/sbin/cleanerd/cleanerd.c
> +++ b/sbin/cleanerd/cleanerd.c
> @@ -592,7 +592,7 @@ nilfs_cleanerd_select_segments(struct nilfs_cleanerd *cleanerd,
>  	 * selected. */
>  	thr = (config->cf_selection_policy.p_threshold != 0) ?
>  		config->cf_selection_policy.p_threshold :
> -		sustat->ss_nongc_ctime;
> +		~0ULL;
>  

As I understand the code of nilfs_cleanerd, this code is correct without
your changing. The ss_nongc_ctime is the creation time of the last
segment not for GC. When thr is set then it compared with sui_lastmod.
The sui_lastmod is the timestamp of last modification. So, the
nilfs_cleanerd works right.

I think that this is a bug on the kernel side. My current vision is that
in some environment the ns_nongc_ctime can be not updated correctly. So,
you have such threshold that prevent from segments clearing.

Thank you for the issue report.

With the best regards,
Vyacheslav Dubeyko.

>  	for (segnum = 0; segnum < sustat->ss_nsegs; segnum += n) {
>  		count = (sustat->ss_nsegs - segnum < NILFS_CLEANERD_NSUINFO) ?


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