Faster mountinfo parser

[kolyshkin]

This is part 1 of improving runc wrt /proc/self/mountinfo parsing.

It needs improvements because

• the current code has 5 different implementations of runc parser
• a single runc run command reads mountinfo from from 72 to 116 times (depending on whether --systemd-cgroup is set) on my system.
• reading mountinfo from the kernel might be slow if there are many containers running (and thus many mounts)
• reading mountinfo might be racy (see https://github.com/kolyshkin/procfs-test)

This PR

• updates the mountinfo parsing code (which was originally taken from Docker) to the recent code from Moby, making it way faster and versatile. For background on those improvements, see
  • pkg/mount improvements moby/moby#36091
  • fix parseInfoFile does not handle spaces in filenames moby/moby#38977
  • Yet better mountinfo parser moby/moby#40684
• converts existing users to benefit from it.

My plans are

• part 2: switch the code that parses mountinfo on its own to use this package
• part 3: look into cgroups code, trying to minimize calls to parse mountinfo

[AkihiroSuda]

Do you have benchmark results?

[kolyshkin]

Do you have benchmark results?

I have just updated the description. Haven't performed any benchmarks for this one, but e.g. moby/moby#36091 claims 8x speed improvement :)

[AkihiroSuda]

Maybe we should begin with splitting the repo first moby/moby#40684 (comment)

[kolyshkin]

@AkihiroSuda is it OK to have runc depend on moby repos? I am asking because commit 3ca4c78 specifically says "get rid of docker/docker dependency". Or is a dependency upon a smaller thing is fine?

[AkihiroSuda]

Or is a dependency upon a smaller thing is fine?

I think fine

[crosbymichael]

no, we don't want to dependency on moby/moby. moby already imports runc and we don't want it to be the other way around. keep the code here :)

[kolyshkin]

no, we don't want to dependency on moby/moby. moby already imports runc and we don't want it to be the other way around. keep the code here :)

I never proposed a dependency on moby/moby, this is out of the question.

I don't like copy-pasting code around either (as it creates a maintenance nightmare -- instead of fixing the code in one place, it has to be fixed in a few).

So, for now I have split out moby/moby/pkg/mount to two new packages:

• github.com/moby/sys/mount
• github.com/moby/sys/mountinfo
  and made moby use it (part I: switch to moby/sys/{mount,mountinfo} part I moby/moby#40691, part II: switch to moby/sys/{mount,mountinfo} part II moby/moby#40694)

Anyway, moving along according to the new plan: #2256

[kolyshkin]

replaced by #2256