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.
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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.
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