Am 24.07.2018 um 10:28 schrieb Coly Li:
On 2018/7/24 3:16 PM, Stefan Priebe - Profihost AG wrote:
Am 24.07.2018 um 06:03 schrieb Coly Li:
Commit b1092c9af9ed ("bcache: allow quick writeback when backing idle") allows the writeback rate to be faster if there is no I/O request on a bcache device. It works well if there is only one bcache device attached to the cache set. If there are many bcache devices attached to a cache set, it may introduce performance regression because multiple faster writeback threads of the idle bcache devices will compete the btree level locks with the bcache device who have I/O requests coming.
This patch fixes the above issue by only permitting fast writebac when all bcache devices attached on the cache set are idle. And if one of the bcache devices has new I/O request coming, minimized all writeback throughput immediately and let PI controller __update_writeback_rate() to decide the upcoming writeback rate for each bcache device.
Also when all bcache devices are idle, limited wrieback rate to a small number is wast of thoughput, especially when backing devices are slower non-rotation devices (e.g. SATA SSD). This patch sets a max writeback rate for each backing device if the whole cache set is idle. A faster writeback rate in idle time means new I/Os may have more available space for dirty data, and people may observe a better write performance then.
Please note bcache may change its cache mode in run time, and this patch still works if the cache mode is switched from writeback mode and there is still dirty data on cache.
Fixes: Commit b1092c9af9ed ("bcache: allow quick writeback when backing idle") Cc: stable@vger.kernel.org #4.16+ Signed-off-by: Coly Li colyli@suse.de Tested-by: Kai Krakow kai@kaishome.de Cc: Michael Lyle mlyle@lyle.org Cc: Stefan Priebe s.priebe@profihost.ag
Hi Coly,
i'm still experiencing the same bug as yesterday while rebooting every two times i get a deadlock in cache_set_free.
Sadly it's so late ion the shutdown process that netconsole is already unloaded or at least i get no messages from while it happens. The traces look the same like yesterday.
Hi Stefan,
Do you use the v2 patch on latest SLE15 kernel source?
Yes - i use the kernel code from here: https://github.com/openSUSE/kernel-source/commits/SLE15
Let me try to reproduce it on my machine. I assume when you reboot, the cache is still dirty and not clean up, am I right ?
Yes with around 15GB of dirty data - ceph is running on top of it and generated many random writes.
And which file system do you mount on top of the bcache device ?
XFS
Thanks.
Coly Li
Greets, Stefan