** Also affects: linux (Ubuntu Yakkety)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Zesty)
Importance: Medium
Assignee: Colin Ian King (colin-king)
Status: In Progress
** Changed in: linux (Ubuntu Yakkety)
Status: New => In Progress
** Changed in: linux (Ubuntu Yakkety)
Assignee: (unassigned) => Colin Ian King (colin-king)
** Changed in: linux (Ubuntu Zesty)
Status: In Progress => Fix Released
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https://bugs.launchpad.net/bugs/1649905
Title:
On boot excessive number of kworker threads are running
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Yakkety:
In Progress
Status in linux source package in Zesty:
Fix Released
Bug description:
[SRU REQUEST, Yakkety]
Ubuntu Yakkety 4.8 kernels have an excessive amount of kworker threads
running, this is especially noticeable on boot, one can easily have >
1000 kworker threads on a 4 CPU box.
Bisected this down to:
commit 81ae6d03952c1bfb96e1a716809bd65e7cd14360
Author: Vladimir Davydov <[email protected]>
Date: Thu May 19 17:10:34 2016 -0700
mm/slub.c: replace kick_all_cpus_sync() with synchronize_sched() in
kmem_cache_shrink()
[FIX]
The synchronize_sched calls seem to create all these excessive kworker
threads. This is fixed with upstream commit:
commit 89e364db71fb5e7fc8d93228152abfa67daf35fa
Author: Vladimir Davydov <[email protected]>
Date: Mon Dec 12 16:41:32 2016 -0800
slub: move synchronize_sched out of slab_mutex on shrink
synchronize_sched() is a heavy operation and calling it per each cache
owned by a memory cgroup being destroyed may take quite some time. What
is worse, it's currently called under the slab_mutex, stalling all works
doing cache creation/destruction.
Actually, there isn't much point in calling synchronize_sched() for each
cache - it's enough to call it just once - after setting cpu_partial for
all caches and before shrinking them. This way, we can also move it out
of the slab_mutex, which we have to hold for iterating over the slab
cache list.
[TEST CASE]
Without the fix, boot a Yakkety and count the number of kthreads:
ps -ef | grep kworker | wc -l
1034
With the fix, boot count the number kthreads and it will be
dramatically less:
ps -ef | grep kworker | wc -l
32
Since this touches the slub allocator and cgroups too, I have
regression tested this against the kernel-team autotest regression
tests to sanity check this fix. All seems OK.
Note: this only affects kernels from 4.7-rc1 through to 4.8
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