This series replaces mm/page_alloc's per-cpu page lists drain mechanism with one that allows accessing the lists remotely. Currently, only a local CPU is permitted to change its per-cpu lists, and it's expected to do so, on-demand, whenever a process demands it by means of queueing a drain task on the local CPU. This causes problems for NOHZ_FULL CPUs and real-time systems that can't take any sort of interruption and to some lesser extent inconveniences idle and virtualised systems. The new algorithm will atomically switch the pointer to the per-cpu page lists and use RCU to make sure it's not being concurrently used before draining the lists. And its main benefit of is that it fixes the issue for good, avoiding the need for configuration based heuristics or having to modify applications (i.e. using the isolation prctrl being worked by Marcello Tosatti ATM). All this with minimal performance implications: a page allocation microbenchmark was run on multiple systems and architectures generally showing no performance differences, only the more extreme cases showed a 1-3% degradation. See data below. Needless to say that I'd appreciate if someone could validate my values independently. The approach has been stress-tested: I forced 100 drains/s while running mmtests' pft in a loop for a full day on multiple machines and archs (arm64, x86_64, ppc64le). Note that this is not the first attempt at fixing this per-cpu page lists: - The first attempt[1] tried to conditionally change the pagesets locking scheme based the NOHZ_FULL config. It was deemed hard to maintain as the NOHZ_FULL code path would be rarely tested. Also, this only solves the issue for NOHZ_FULL setups, which isn't ideal. - The second[2] unanimously switched the local_locks to per-cpu spinlocks. The performance degradation was too big. Previous RFC: https://lkml.org/lkml/2021/10/8/793 Thanks! [1] https://lkml.org/lkml/2021/9/21/599 [2] https://lkml.org/lkml/2021/11/3/644 --- Changes since RFC: - Get rid of aesthetic changes that affected performance - Add more documentation - Add better commit messages - Pass sparse tests - Verify this_cpu_*() usage - Performance measurements Nicolas Saenz Julienne (2): mm/page_alloc: Access lists in 'struct per_cpu_pages' indirectly mm/page_alloc: Add remote draining support to per-cpu lists include/linux/mmzone.h | 28 +++++- mm/page_alloc.c | 212 ++++++++++++++++++++++++++--------------- mm/vmstat.c | 6 +- 3 files changed, 162 insertions(+), 84 deletions(-) -------------------------Performance results----------------------------- I'm focusing on mmtests' Page Fault Test (pft), as it's page allocator intensive. - AMD Daytona Reference System, 2 sockets, AMD EPYC 7742, Zen 2, 64-Core, 4 NUMA nodes, x86_64 pft timings: vanilla rcu Amean system-1 58.52 ( 0.00%) 58.92 * -0.68%* Amean system-4 61.00 ( 0.00%) 61.41 * -0.67%* Amean system-7 61.55 ( 0.00%) 61.74 * -0.30%* Amean system-12 64.91 ( 0.00%) 64.94 * -0.05%* Amean system-21 98.80 ( 0.00%) 99.92 * -1.13%* Amean system-30 147.68 ( 0.00%) 145.83 * 1.25%* Amean system-48 237.04 ( 0.00%) 241.29 * -1.79%* Amean system-79 286.61 ( 0.00%) 283.72 * 1.01%* Amean system-110 303.40 ( 0.00%) 299.91 * 1.15%* Amean system-128 345.07 ( 0.00%) 342.10 * 0.86%* Amean elapsed-1 61.21 ( 0.00%) 61.65 * -0.71%* Amean elapsed-4 15.94 ( 0.00%) 16.05 * -0.69%* Amean elapsed-7 9.24 ( 0.00%) 9.28 * -0.47%* Amean elapsed-12 5.70 ( 0.00%) 5.70 * -0.07%* Amean elapsed-21 5.11 ( 0.00%) 5.06 * 1.13%* Amean elapsed-30 5.28 ( 0.00%) 5.14 * 2.73%* Amean elapsed-48 5.28 ( 0.00%) 5.24 * 0.74%* Amean elapsed-79 4.41 ( 0.00%) 4.31 * 2.17%* Amean elapsed-110 3.45 ( 0.00%) 3.44 * 0.40%* Amean elapsed-128 2.75 ( 0.00%) 2.75 * -0.28%* - AMD Speedway Reference System, 2 sockets, AMD EPYC 7601, Zen 1, 64-core, 8 NUMA nodes, x86_64. Lots of variance between tests on this platform. It'll easily swing -+5% on each result. pft timings: vanilla rcu Amean system-1 69.20 ( 0.00%) 66.21 * 4.32%* Amean system-4 70.79 ( 0.00%) 69.01 * 2.52%* Amean system-7 71.34 ( 0.00%) 69.16 * 3.05%* Amean system-12 74.00 ( 0.00%) 72.74 * 1.70%* Amean system-21 86.01 ( 0.00%) 85.70 * 0.36%* Amean system-30 89.21 ( 0.00%) 89.93 * -0.80%* Amean system-48 92.39 ( 0.00%) 92.43 * -0.04%* Amean system-79 120.19 ( 0.00%) 121.30 * -0.92%* Amean system-110 172.79 ( 0.00%) 179.37 * -3.81%* Amean system-128 201.70 ( 0.00%) 212.57 * -5.39%* Amean elapsed-1 72.23 ( 0.00%) 69.29 * 4.08%* Amean elapsed-4 18.69 ( 0.00%) 18.28 * 2.20%* Amean elapsed-7 10.80 ( 0.00%) 10.54 * 2.41%* Amean elapsed-12 6.62 ( 0.00%) 6.53 * 1.30%* Amean elapsed-21 4.68 ( 0.00%) 4.69 * -0.14%* Amean elapsed-30 3.44 ( 0.00%) 3.50 * -1.66%* Amean elapsed-48 2.40 ( 0.00%) 2.42 * -1.00%* Amean elapsed-79 2.05 ( 0.00%) 2.09 * -1.90%* Amean elapsed-110 1.83 ( 0.00%) 1.91 * -4.60%* Amean elapsed-128 1.75 ( 0.00%) 1.85 * -5.99%* - IBM 9006-22C system, 2 sockets, POWER9, 64-Core, 1 NUMA node per cpu, pppc64le. pft timings: vanilla rcu Amean system-1 1.82 ( 0.00%) 1.85 * -1.43%* Amean system-4 2.18 ( 0.00%) 2.22 * -2.02%* Amean system-7 3.27 ( 0.00%) 3.28 * -0.15%* Amean system-12 5.22 ( 0.00%) 5.20 * 0.26%* Amean system-21 10.10 ( 0.00%) 10.20 * -1.00%* Amean system-30 15.00 ( 0.00%) 14.52 * 3.20%* Amean system-48 26.41 ( 0.00%) 25.96 * 1.71%* Amean system-79 29.35 ( 0.00%) 29.70 * -1.21%* Amean system-110 24.01 ( 0.00%) 23.40 * 2.54%* Amean system-128 24.57 ( 0.00%) 25.32 * -3.06%* Amean elapsed-1 1.85 ( 0.00%) 1.87 * -1.28%* Amean elapsed-4 0.56 ( 0.00%) 0.57 * -1.72%* Amean elapsed-7 0.51 ( 0.00%) 0.50 * 0.07%* Amean elapsed-12 0.51 ( 0.00%) 0.51 * 0.06%* Amean elapsed-21 0.54 ( 0.00%) 0.54 * 0.06%* Amean elapsed-30 0.54 ( 0.00%) 0.53 * 2.22%* Amean elapsed-48 0.58 ( 0.00%) 0.57 * 1.73%* Amean elapsed-79 0.49 ( 0.00%) 0.48 * 0.89%* Amean elapsed-110 0.37 ( 0.00%) 0.37 * -1.08%* Amean elapsed-128 0.33 ( 0.00%) 0.33 * 0.00%* - Ampere MtSnow, 1 socket, Neoverse-N1, 80-Cores, 1 NUMA node, arm64. pft timings: vanilla rcu Amean system-1 11.92 ( 0.00%) 11.99 * -0.61%* Amean system-4 13.13 ( 0.00%) 13.09 * 0.31%* Amean system-7 13.91 ( 0.00%) 13.94 * -0.20%* Amean system-12 15.77 ( 0.00%) 15.69 * 0.48%* Amean system-21 21.32 ( 0.00%) 21.42 * -0.46%* Amean system-30 28.58 ( 0.00%) 29.12 * -1.90%* Amean system-48 47.41 ( 0.00%) 46.91 * 1.04%* Amean system-79 76.76 ( 0.00%) 77.16 * -0.52%* Amean system-80 77.98 ( 0.00%) 78.23 * -0.32%* Amean elapsed-1 12.46 ( 0.00%) 12.53 * -0.58%* Amean elapsed-4 3.47 ( 0.00%) 3.46 * 0.34%* Amean elapsed-7 2.18 ( 0.00%) 2.21 * -1.58%* Amean elapsed-12 1.41 ( 0.00%) 1.42 * -0.80%* Amean elapsed-21 1.09 ( 0.00%) 1.12 * -2.60%* Amean elapsed-30 0.98 ( 0.00%) 1.01 * -3.08%* Amean elapsed-48 1.08 ( 0.00%) 1.10 * -1.78%* Amean elapsed-79 1.32 ( 0.00%) 1.28 * 2.71%* Amean elapsed-80 1.32 ( 0.00%) 1.28 * 3.23%* - Dell R430, 2 sockets, Intel Xeon E5-2640 v3, Sandy Bridge, 16-Cores, 2 NUMA nodes, x86_64. pft timings: vanilla rcu Amean system-1 11.10 ( 0.00%) 11.07 * 0.24%* Amean system-3 11.14 ( 0.00%) 11.10 * 0.34%* Amean system-5 11.18 ( 0.00%) 11.13 * 0.47%* Amean system-7 11.21 ( 0.00%) 11.17 * 0.38%* Amean system-12 11.28 ( 0.00%) 11.28 ( -0.03%) Amean system-18 13.24 ( 0.00%) 13.25 * -0.11%* Amean system-24 17.12 ( 0.00%) 17.14 ( -0.13%) Amean system-30 21.10 ( 0.00%) 21.23 * -0.60%* Amean system-32 22.31 ( 0.00%) 22.47 * -0.71%* Amean elapsed-1 11.76 ( 0.00%) 11.73 * 0.29%* Amean elapsed-3 3.93 ( 0.00%) 3.93 * 0.17%* Amean elapsed-5 2.39 ( 0.00%) 2.37 * 0.74%* Amean elapsed-7 1.72 ( 0.00%) 1.71 * 0.81%* Amean elapsed-12 1.02 ( 0.00%) 1.03 ( -0.42%) Amean elapsed-18 1.13 ( 0.00%) 1.14 ( -0.18%) Amean elapsed-24 0.87 ( 0.00%) 0.88 * -0.65%* Amean elapsed-30 0.77 ( 0.00%) 0.78 * -0.86%* Amean elapsed-32 0.74 ( 0.00%) 0.74 ( 0.00%) - HPE Apollo 70, 2 sockets, Cavium ThunderX2, 128-Cores, 2 NUMA nodes, arm64. NOTE: The test here only goes up to 128 for some reason, although there are 256 CPUs. Maybe a mmtests issue? I didn't investigate. pft timings: vanilla rcu Amean system-1 4.42 ( 0.00%) 4.36 * 1.29%* Amean system-4 4.56 ( 0.00%) 4.51 * 1.05%* Amean system-7 4.63 ( 0.00%) 4.65 * -0.42%* Amean system-12 5.96 ( 0.00%) 6.02 * -1.00%* Amean system-21 10.97 ( 0.00%) 11.01 * -0.32%* Amean system-30 16.01 ( 0.00%) 16.04 * -0.19%* Amean system-48 26.81 ( 0.00%) 26.78 * 0.09%* Amean system-79 30.80 ( 0.00%) 30.85 * -0.16%* Amean system-110 31.87 ( 0.00%) 31.93 * -0.19%* Amean system-128 36.27 ( 0.00%) 36.31 * -0.10%* Amean elapsed-1 4.88 ( 0.00%) 4.85 * 0.60%* Amean elapsed-4 1.27 ( 0.00%) 1.26 * 1.00%* Amean elapsed-7 0.73 ( 0.00%) 0.74 * -0.46%* Amean elapsed-12 0.55 ( 0.00%) 0.55 * 1.09%* Amean elapsed-21 0.59 ( 0.00%) 0.60 * -0.96%* Amean elapsed-30 0.60 ( 0.00%) 0.60 * 0.28%* Amean elapsed-48 0.60 ( 0.00%) 0.60 * 0.44%* Amean elapsed-79 0.49 ( 0.00%) 0.49 * -0.07%* Amean elapsed-110 0.36 ( 0.00%) 0.36 * 0.28%* Amean elapsed-128 0.31 ( 0.00%) 0.31 * -0.43%* - Raspberry Pi 4, 1 socket, bcm2711, Cortex-A72, 4-Cores, 1 NUMA node, arm64. pft timings: vanilla rcu Amean system-1 0.67 ( 0.00%) 0.67 * -1.25%* Amean system-3 1.30 ( 0.00%) 1.29 * 0.62%* Amean system-4 1.61 ( 0.00%) 1.59 * 0.95%* Amean elapsed-1 0.71 ( 0.00%) 0.72 * -1.17%* Amean elapsed-3 0.45 ( 0.00%) 0.45 * 0.88%* Amean elapsed-4 0.42 ( 0.00%) 0.42 * 1.19%* -- 2.34.1
