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Message #15779
[Bug 1226726] Re: dentry_reset_mounted walks entire mount list holding vfsmount write lock
This script will test performance of 'ip netns exec <ns> /bin/true" when
increasing namespaces by 1000.
** Attachment added: "test_ns.sh"
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1226726/+attachment/3825692/+files/test_ns.sh
** Also affects: linux (Ubuntu Precise)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Quantal)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Saucy)
Importance: Medium
Assignee: Chris J Arges (arges)
Status: New
** Also affects: linux (Ubuntu Raring)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Raring)
Assignee: (unassigned) => Chris J Arges (arges)
** Changed in: linux (Ubuntu Quantal)
Assignee: (unassigned) => Chris J Arges (arges)
** Changed in: linux (Ubuntu Precise)
Assignee: (unassigned) => Chris J Arges (arges)
** Changed in: linux (Ubuntu Precise)
Importance: Undecided => Medium
** Changed in: linux (Ubuntu Quantal)
Importance: Undecided => Medium
** Changed in: linux (Ubuntu Raring)
Importance: Undecided => Medium
** Changed in: linux (Ubuntu Saucy)
Importance: Medium => Undecided
** Changed in: linux (Ubuntu Saucy)
Assignee: Chris J Arges (arges) => (unassigned)
** Changed in: linux (Ubuntu Saucy)
Status: New => Fix Released
** Changed in: linux (Ubuntu Precise)
Status: New => In Progress
** Changed in: linux (Ubuntu Quantal)
Status: New => In Progress
** Changed in: linux (Ubuntu Raring)
Status: New => In Progress
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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:
In Progress
Status in “linux” source package in Quantal:
In Progress
Status in “linux” source package in Raring:
In Progress
Status in “linux” source package in Saucy:
Fix Released
Bug description:
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.
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References