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d29bd8efe1
Add a small selftest that stresses pipe->mutex contention by spawning N writer threads that hammer a single pipe with multi-page writes, plus M reader threads that drain. Each writer records its own write() latency samples into a log2-bucketed histogram; main aggregates and prints total writes, throughput, average and percentile (p50/p99) latencies, and the maximum observed latency. Pass --memory-pressure to fork stress-ng (--vm 4 --vm-bytes 80% --vm-method all) for the duration of the run, so alloc_page() in anon_pipe_write() routinely hits direct reclaim. The flag fails fast if stress-ng is not on $PATH. Program print something like the following, for different writes, readers, msgsizes and memory pressure: config: writers=X readers=Y msgsize=Z duration=3 pipe_size=1048576 memory_pressure=[no|yes] writes: total=54451 rate=18150/s throughput_MBps: 1134.40 lat_avg_ns: 275355 lat_p50_ns_upper: 262143 lat_p99_ns_upper: 1048575 lat_max_ns: 2145633 Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Breno Leitao <leitao@debian.org> Link: https://patch.msgid.link/20260524-fix_pipe-v3-2-bb4a75d23a90@debian.org Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>