Re: [PATCH v4 bpf-next/net 5/5] selftest: bpf: Add test for SK_BPF_MEMCG_SOCK_ISOLATED.

On Wed, Sep 3, 2025 at 9:59 AM Kuniyuki Iwashima [off-list ref] wrote:

On Tue, Sep 2, 2025 at 1:49 PM Kuniyuki Iwashima [off-list ref] wrote:

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On Tue, Sep 2, 2025 at 1:26 PM Martin KaFai Lau [off-list ref] wrote:

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On 8/28/25 6:00 PM, Kuniyuki Iwashima wrote:

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The test does the following for IPv4/IPv6 x TCP/UDP sockets
with/without BPF prog.

   1. Create socket pairs
   2. Send a bunch of data that requires more than 256 pages
   3. Read memory_allocated from the 3rd column in /proc/net/protocols
   4. Check if unread data is charged to memory_allocated

If BPF prog is attached, memory_allocated should not be changed,
but we allow a small error (up to 10 pages) in case other processes
on the host use some amounts of TCP/UDP memory.

At 2., the test actually sends more than 1024 pages because the sysctl
net.core.mem_pcpu_rsv is 256 is by default, which means 256 pages are
buffered per cpu before reporting to sk->sk_prot->memory_allocated.

   BUF_SINGLE (1024) * NR_SEND (64) * NR_SOCKETS (64) / 4096
   = 1024 pages

When I reduced it to 512 pages, the following assertion for the
non-isolated case got flaky.

   ASSERT_GT(memory_allocated[1], memory_allocated[0] + 256, ...)

Another contributor to slowness is 150ms sleep to make sure 1 RCU
grace period passes because UDP recv queue is destroyed after that.

There is a kern_sync_rcu() in testing_helpers.c.

Nice helper :)  Will use it.

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   # time ./test_progs -t sk_memcg
   #370/1   sk_memcg/TCP       :OK
   #370/2   sk_memcg/UDP       :OK
   #370/3   sk_memcg/TCPv6     :OK
   #370/4   sk_memcg/UDPv6     :OK
   #370     sk_memcg:OK
   Summary: 1/4 PASSED, 0 SKIPPED, 0 FAILED

   real       0m1.214s
   user       0m0.014s
   sys        0m0.318s

Thanks. It finished much faster in my setup also comparing with the earlier
revision. However, it is a bit flaky when I run it in a loop:

check_isolated:FAIL:not isolated unexpected not isolated: actual 861 <= expected 861

I usually can hit this at ~40-th iteration.

Oh.. I tested ~10 times manually but will try in a tight loop.

This didn't reproduce on my QEMU with/without --enable-kvm.

Changing the assert from _GT to _GE will address the very case
above, but I'm not sure if it's enough.

I doubled NR_SEND and it was still faster with kern_sync_rcu()
than usleep(), so I'll simply double NR_SEND in v5

# time ./test_progs -t sk_memcg
...
Summary: 1/4 PASSED, 0 SKIPPED, 0 FAILED
real 0m0.483s
user 0m0.010s
sys 0m0.191s

Does the bpf CI run tests repeatedly or is this only a manual
scenario ?