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Eric Dumazet says:
====================
net: speedup netns dismantles
From: Eric Dumazet <edumazet@google.com>
In this series, I made network namespace deletions more scalable,
by 4x on the little benchmark described in this cover letter.
- Remove bottleneck on ipv6 addrconf, by replacing a global
hash table to a per netns one.
- Rework many (struct pernet_operations)->exit() handlers to
exit_batch() ones. This removes many rtnl acquisitions,
and gives to cleanup_net() kind of a priority over rtnl
ownership.
Tested on a host with 24 cpus (48 HT)
Test script:
for nr in {1..10}
do
(for i in {1..10000}; do unshare -n /bin/bash -c "ifconfig lo up"; done) &
done
wait
for i in {1..10}
do
sleep 1
echo 3 >/proc/sys/vm/drop_caches
grep net_namespace /proc/slabinfo
done
Before: We can see host struggles to clean the netns, even after there are no new creations.
Memory cost is high, because each netns consumes a good amount of memory.
time ./unshare10.sh
net_namespace 82634 82634 3968 1 1 : tunables 24 12 8 : slabdata 82634 82634 0
net_namespace 82634 82634 3968 1 1 : tunables 24 12 8 : slabdata 82634 82634 0
net_namespace 82634 82634 3968 1 1 : tunables 24 12 8 : slabdata 82634 82634 0
net_namespace 82634 82634 3968 1 1 : tunables 24 12 8 : slabdata 82634 82634 0
net_namespace 82634 82634 3968 1 1 : tunables 24 12 8 : slabdata 82634 82634 0
net_namespace 82634 82634 3968 1 1 : tunables 24 12 8 : slabdata 82634 82634 0
net_namespace 82634 82634 3968 1 1 : tunables 24 12 8 : slabdata 82634 82634 0
net_namespace 82634 82634 3968 1 1 : tunables 24 12 8 : slabdata 82634 82634 0
net_namespace 82634 82634 3968 1 1 : tunables 24 12 8 : slabdata 82634 82634 0
net_namespace 37214 37792 3968 1 1 : tunables 24 12 8 : slabdata 37214 37792 192
real 6m57.766s
user 3m37.277s
sys 40m4.826s
After: We can see the script completes much faster,
the kernel thread doing the cleanup_net() keeps up just fine.
Memory cost is not too big.
time ./unshare10.sh
net_namespace 9945 9945 4096 1 1 : tunables 24 12 8 : slabdata 9945 9945 0
net_namespace 4087 4665 4096 1 1 : tunables 24 12 8 : slabdata 4087 4665 192
net_namespace 4082 4607 4096 1 1 : tunables 24 12 8 : slabdata 4082 4607 192
net_namespace 234 761 4096 1 1 : tunables 24 12 8 : slabdata 234 761 192
net_namespace 224 751 4096 1 1 : tunables 24 12 8 : slabdata 224 751 192
net_namespace 218 745 4096 1 1 : tunables 24 12 8 : slabdata 218 745 192
net_namespace 193 667 4096 1 1 : tunables 24 12 8 : slabdata 193 667 172
net_namespace 167 609 4096 1 1 : tunables 24 12 8 : slabdata 167 609 152
net_namespace 167 609 4096 1 1 : tunables 24 12 8 : slabdata 167 609 152
net_namespace 157 609 4096 1 1 : tunables 24 12 8 : slabdata 157 609 152
real 1m43.876s
user 3m39.728s
sys 7m36.342s
====================
Link: https://lore.kernel.org/r/20220208045038.2635826-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.