Messages in this thread | | | Date | Thu, 15 May 2014 11:42:37 +0200 | From | Mateusz Guzik <> | Subject | Re: [PATCH 2/2] fs: print a message when freezing/unfreezing filesystems |
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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.
So general idea is to support providing callbacks when setting tasks to TASK_UNINTERRUPTIBLE which could either tell the user what's up directly or would perform some heuristics. I'll post this in a separate thread later, maybe with PoC.
Thanks, -- Mateusz Guzik
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