Re: bcache hangs on writes, recovers after disabling discard on cache device

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On Thu, 11 Jul 2013, Kent Overstreet wrote:

On Thu, Jul 11, 2013 at 05:58:17PM +0300, Juha Aatrokoski wrote:
On Mon, 24 Jun 2013, Heiko Wundram wrote:

In a rather old thread of mine (514C4FC1.6090804@xxxxxxxxxxxxx), I
already stated a problem I was seeing back at the time, namely
that bcache seems to hang on writes to the SSD device after some
time, writing 50 MB/s continuously to the output device.
...
Disabling discard on the SSD device (by echo 0 >
/sys/fs/bcache/.../cache0/discard) makes the bcache device become
responsive again.

I can confirm this. On Monday I booted into kernel 3.8.13-gentoo
with the current "bcache" branch patched onto it. Discard was on for
the cache device, and today this 50MB/s hang occured. Disabling
discard did indeed fix it.

I had CONFIG_BCACHE_CLOSURES_DEBUG=y in the kernel, and the contents
of /sys/kernel/debug/bcache/bcache-UUID and
/sys/kernel/debug/closures both before and after disabling discard
can be found at the address below, in case they can help in
determining where exactly the hang happens.

Can you give this patch a try? It's on top of the current
bcache-for-3.11 branch

OK, now running the same kernel with this patch applied and discard enabled. However, it has previously taken my system 2-4 days to trigger this bug, so I'd say at least two weeks before I can say the patch (may have) fixed the issue.

Heiko, can your setup reproduce this bug consistently in a shorter time? If so, you could also try this patch for faster feedback.

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