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libct/cg/fs2.GetStats() improvements #2873

Merged
merged 7 commits into from
Apr 19, 2021
Merged

libct/cg/fs2.GetStats() improvements #2873

merged 7 commits into from
Apr 19, 2021

Commits on Mar 31, 2021

  1. libct/cg/fs2/memory: fix swap reporting 

    cgroup v1 reports combined mem+swap in stats.MemoryStats.SwapUsage.
In cgroup v2, swap is separate.

For the sake of compatibility, make v2 report mem+swap as well.
This also includes Limit.

Signed-off-by: Kir Kolyshkin <[email protected]>
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  2. libct/cg/fs[2]/getMemoryData[V2]: optimize 

    Existing code ignores ENOENT error in case we're reading data from
controls that might not be enabled. While this is correct, the code
can be improved:

1. Check name != "" instead of moduleName != "memory", as these checks
   are equivalent but the new one is faster.

2. It does not make sense to ignore subsequent errors -- if the control
   is not available, we won't hit this codepath.

3. Add a comment explaining why we ignore the error.

Signed-off-by: Kir Kolyshkin <[email protected]>
    @kolyshkin
    kolyshkin committed Mar 31, 2021
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  3. libct/cg/fs2/memory.Stat: add usage for root cgroup 

    There is no memory.{current,max} for the root node in cgroup v2, and
thus stats for "/sys/fs/cgroup" return an error.

The same thing works with cgroup v1 (as there are
memory.{usage,limit}_in_bytes files in the root node).

Emulate stats for /sys/fs/cgroup by getting numbers from
/proc/self/meminfo.

NOTE that both memory.current (in cgroup v2) and memory.usage_in_bytes
(in cgroup v1) include page cache etc into the number, so we do the same
when calculating memory usage (as opposed to number reported by "free",
which excludes page cache and buffers).

[v2: check for cgroup files first, as future kernels might add it]
[v3: don't subtract cache from mem_used, simplifying the logic]

[Initially, I wanted to avoid parsing yet another /proc file and
instead mock some numbers using data from memory.stat but was
unable to come up with formulae that make sense.]

Signed-off-by: Kir Kolyshkin <[email protected]>
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  4. libct/cg/fs2.Stat: always call statCpu 

    Giuseppe found out that cpu.stat for a cgroup is available even if
the cpu controller is not enabled for it. So, let's call statCpu
regradress, and ignore ENOENT.

Signed-off-by: Kir Kolyshkin <[email protected]>
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  5. libct/cg/fs2/getPidsWithoutController: optimize 

    It is inefficient to create an associative map for the whole purpose of
counting the number of elements in it, especially if the elements are
all unique. It uses more CPU than necessary and creates some work for
the garbage collector.

The file we read contains PIDs and newlines, and the easiest/fastest way
to get the number of PIDs is just to count the newlines.

Signed-off-by: Kir Kolyshkin <[email protected]>
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  6. libct/cg/fs2.statPids: fall back directly 

    When getting pids stats, instead of checking whether the pids controller
is available, let's use a fall back function in case pids.current does
not exist. This simplifies the logic in fs2.GetStats.

Signed-off-by: Kir Kolyshkin <[email protected]>
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  7. libct/cg/fs2.Stat: don't look for available controllers 

    Some controllers might still have stats available even if they are
disabled (this is definitely so for cpu.stat -- see earlier commit).

Some stat methods might implement sensible fallbacks (see previous
commit for statPids.

In the view of all that, it makes sense to not check if a particular
controller is available, but rather ignore ENOENT from it.

Signed-off-by: Kir Kolyshkin <[email protected]>
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