On Thu, 15 May 2014, Jan Kara wrote: > Date: Thu, 15 May 2014 12:01:57 +0200 > From: Jan Kara <jack@xxxxxxx> > To: Mateusz Guzik <mguzik@xxxxxxxxxx> > Cc: Dave Chinner <david@xxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, > linux-fsdevel@xxxxxxxxxxxxxxx, Josef Bacik <jbacik@xxxxxx>, > Jan Kara <jack@xxxxxxx>, Al Viro <viro@xxxxxxxxxxxxxxxxxx>, > Eric Sandeen <esandeen@xxxxxxxxxx> > Subject: Re: [PATCH 2/2] fs: print a message when freezing/unfreezing > filesystems > > On Thu 15-05-14 11:42:37, Mateusz Guzik wrote: > > On Thu, May 15, 2014 at 07:54:57AM +1000, Dave Chinner wrote: > > > On Tue, May 13, 2014 at 08:31:02PM +0200, Mateusz Guzik wrote: > > > > This helps hang troubleshooting efforts when only dmesg is available. > > > > > > I really don't think that spamming dmesg every time a filesystem is > > > frozen or thawed is a good idea. This happens a *lot* when systems > > > are using snapshots, and for the most part nobody cares about > > > freeze/thaw cycles because they almost always work just fine. > > > > > > > I agree it may get noisy. > > > > > I'd think that /proc/self/mounts would be a much better place to > > > indicate that the fs is frozen. After all, that's where we tell > > > people whether the filesystem is ro or rw, and frozen is just > > > a temporary, non-invasive ro state... > > > > > > > Except you can't inspect /proc/self/mounts when the only thing you got > > is dmesg, so this does not really help my case. > > > > That said, I'll try to come up with a different solution. > > > > Poorly reported side-effects of frozen I/O are only a part of the real > > problem which is hung task detector being able to typically report > > backtraces of "victims" only. I came up with printks becuase these are > > a cheap way and would help us out in a lot of cases. > I was tracking down a couple of times what the hell is freezing the > filesystem (and not unfreezing it) and I agree with Mateusz it would be > nice if we could tell after the fact who froze the fs. Maybe we could store > that information in superblock and dump it during emergency thaw? I like that idea and if we agree to create procfs file to list frozen file system this might be one of the useful information to report there. -Lukas > > Honza > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
