Precise 3.2.0-52-virtual large VM: #ns ms 1 103 1001 138 2001 219 3001 374 4001 606 5001 847 6001 921 7001 1438 8001 1734 9001 2099 10001 2441
Precise 3.5.0-43-generic lts-quantal large VM: #ns ms 1 23 1001 45 2001 86 3001 93 4001 171 5001 147 6001 258 7001 403 8001 359 9001 538 10001 386 ** Tags removed: verification-needed-quantal ** Tags added: verification-done-quantal -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1226726 Title: dentry_reset_mounted walks entire mount list holding vfsmount write lock Status in “linux” package in Ubuntu: Fix Released Status in “linux” source package in Precise: Won't Fix Status in “linux” source package in Quantal: Fix Committed Status in “linux” source package in Raring: Fix Committed Status in “linux” source package in Saucy: Fix Released Bug description: 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. The quantal and raring solutions differ but are both based on the 84d17192 patch. The quantal solution does a backport of this patch instead of clean cherry-picks because of the amount of deps required to just use cherry-picks. The raring solution was able to be done with two clean cherry-picks and that's why that solution was chosen. -- 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. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1226726/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
