** Description changed: + SRU Justification: + + Impact: When creating thousands of network namespaces the delay in + executing commands increases exponentially in kernels before 84d17192. + + Fix: In 84d17192 in the upstream kernel, locking code in fs/namespace.c + is greatly improved resulting in much better performance when the number + namespaces increase. + + Testcase: Below, test_ns.sh can be run and a graph can be compared + between the existing version and the patched version. + + Additional Information: Because this is a change in the vfs layer, I ran + the xfstests and compared before and after results of this patch. The + patch did not create any additional failures in the generic xfstests. + + -- + Whenever one enters a network namespace via "ip netns exec foobar somecommand" there is a mount done of the appropriate device on /sys since "somecommand" needs to see namespace specific versions of /sys directories. When the ip process exits these mounts need to be torn down, and that requires a global write lock for vfsmount_lock (this is a single writer multiple reader lock). This has serious performance implications when the number of name spaces increase. The commit 84d17192 addresses this issue, and it is clear by running the attached testcase that it fixes performance issues when dealing with large numbers of namespaces. I've included a graph with the differences in performance between this fix and its parent commit to show the the improve in performance. The x-axis represents the number of namespaces and the y-axis is execution time in ms. After applying the patch the performance delays are not exponentially increasing. This affects 3.2/3.5/3.8 series kernels, as it was fixed in 3.10.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1226726 Title: dentry_reset_mounted walks entire mount list holding vfsmount write lock To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1226726/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
