On Tue, Nov 2, 2021 at 12:58 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Mon 01-11-21 08:44:58, Suren Baghdasaryan wrote: > [...] > > I'm with you on this one, that's why I wanted to measure the price we > > would pay. Below are the test results: > > > > Test: https://lore.kernel.org/all/20170725142626.GJ26723@xxxxxxxxxxxxxx/ > > Compiled: gcc -O2 -static test.c -o test > > Test machine: 128 core / 256 thread 2x AMD EPYC 7B12 64-Core Processor > > (family 17h) > > > > baseline (Linus master, f31531e55495ca3746fb895ffdf73586be8259fa) > > p50 (median) 87412 > > p95 168210 > > p99 190058 > > average 97843.8 > > stdev 29.85% > > > > unconditional mmap_write_lock in exit_mmap (last column is the change > > from the baseline) > > p50 (median) 88312 +1.03% > > p95 170797 +1.54% > > p99 191813 +0.92% > > average 97659.5 -0.19% > > stdev 32.41% > > > > unconditional mmap_write_lock in exit_mmap + Matthew's patch (last > > column is the change from the baseline) > > p50 (median) 88807 +1.60% > > p95 167783 -0.25% > > p99 187853 -1.16% > > average 97491.4 -0.36% > > stdev 30.61% > > > > stdev is quite high in all cases, so the test is very noisy. > > The impact seems quite low IMHO. WDYT? > > Results being very noisy is what I recall as well. Thanks! I believe, despite the noise, the percentiles show that overall we do not noticeably regress the exit path by taking mmap_lock unconditionally. If there are no objections, I would like to post a patchset which implements unconditional locking in exit_mmap() and process_madvise() calling __oom_reap_task_mm() under protection of read mmap_lock. Thanks! > -- > Michal Hocko > SUSE Labs
