cgroups/v1: optimize path usage #2494
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Needs rebase. |
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mrunalp
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Aug 25, 2020
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@AkihiroSuda PTAL |
kolyshkin
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Aug 25, 2020
When paths are set, we only need to place the PID into proper cgroups, and we do know all the paths already. Both fs/d.path() and systemd/v1/getSubsystemPath() parse /proc/self/mountinfo, and the only reason they are used here is to check whether the subsystem is available. Use a much simpler/faster check instead. Frankly, I am not sure why the check is needed at all. Maybe it should be dropped. Also, for fs driver, since d is no longer used in this code path, move its initialization to after it. Signed-off-by: Kir Kolyshkin <[email protected]>
We call joinCgroups() from Apply, and in there we iterate through the list of subsystems, calling getSubsystemPath() for each. This is expensive, since every getSubsystemPath() involves parsing mountinfo. At the end of Apply(), we iterate through the list of subsystems to fill the m.paths, again calling getSubsystemPath() for every subsystem. As a result, we parse mountinfo about 20 times here. Let's find the paths first and reuse m.paths in joinCgroups(). While at it, since join() is just two calls now, inline it. Signed-off-by: Kir Kolyshkin <[email protected]>
In all these cases, getSubsystemPath() was already called, and its result stored in m.paths map. It makes no sense to not reuse it. Signed-off-by: Kir Kolyshkin <[email protected]>
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AkihiroSuda
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| continue | ||
| } | ||
| return err | ||
| // XXX(kolyshkin@): why this check is needed? |
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What happens without this check?
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As far as I can see, nothing bad. The paths map is then used to write pid to cgroups, and WriteCgroupProc has a check that path exists.
There may be other scenarios (with software that uses runc/libcontainer) I don't envision, and I have broken stuff in the past, so I am trying to be extra careful here.
So, ideally, I'd remove this, but maybe later, thus TODO.
The new check is already 100x better than the old one, so this patch is a big improvement -- I'm just not sure if the check is needed at all.
mrunalp
approved these changes
Aug 26, 2020
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@AkihiroSuda PTAL |
AkihiroSuda
approved these changes
Sep 11, 2020
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this is separated out from #2438 in order to make review easier
Limit the use of
getSubsystemPath()andd.path()functions, reusing them.pathsinstead.See individual commit descriptions for details.
Number of times mountinfo was parsed during
runc --systemd-cgroup runof a busybox container runningsleep 1went down from 50 to 19 as a result of these changes.