Dne 13.2.2017 v 15:19 Jonas Degrave napsal(a):
I am on kernel version 4.4.0-62-generic. I cannot upgrade to kernel 4.9, as it did not play nice with CUDA-drivers: https://devtalk.nvidia.com/default/topic/974733/nvidia-linux-driver-367-57-and-up-do-not-install-on-kernel-4-9-0-rc2-and-higher/ <https://devtalk.nvidia.com/default/topic/974733/nvidia-linux-driver-367-57-and-up-do-not-install-on-kernel-4-9-0-rc2-and-higher/> Yes, I understand the cache needs repeated usage of blocks, but my question is basically how many? And if I can lower that number? In our use case, you basically read a certain group of 100GB of data completely about 100 times. Then another user logs in, and reads a different group of data about 100 times. But after a couple of such users, I observe that only 20GB in total has been promoted to the cache. Even though the cache is 450GB big, and could easily fit all the data one user would need. So, I come to the conclusion that I need a more aggressive policy. I now have a reported hit rate of 19.0%, when there is so few data on the volume that 73% of the data would fit in the cache. I could probably solve this issue by making the caching policy more aggressive. I am looking for a way to do that.
There are 2 'knobs' - one is 'sequential_threshold' where cache tries to avoid promoting 'long' continuous reads into cache - so if you do 100G reads then these likely meet the criteria and are avoided from being promoted (and I think this one is not configurable for smq. Other is 'migration_threshold' which limit bandwidth load on cache device. You can try to change its value: lvchange --cachesettings migration_threshold=10000000 vg/cachedlv (check with dmsetup status) Not sure thought how are there things configurable with smq cache policy. Regards Zdenek _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
