Change Details

We currently set the maxcache to 0 on the pgcache uma zone. Under a heavy Netflix workload, this leads to lock contention on the vm page free queue from vm_page_zone_import / vm_page_zone_release. This change adds a tunable to allow the administrator to specify the maxache. On a Netflix 100G cache (16 core / 32t Xeon E5-v4 2697A), we get to about 80Gb/s with CPU maxed contending for the vm page free lock when maxcache is 0. When it is set to 0x60000 we reach 95Gb/s with idle CPU.

We currently set the maxcache to 0 on the pgcache uma zone. Under a heavy Netflix ktls encrypted web workload, this leads to lock contention on the vm page free queue from vm_page_zone_import / vm_page_zone_release as the buckets are frequently drained. This change adds a tunable to allow the administrator to specify the maxache. On a Netflix 100G cache (16 core / 32t Xeon E5-v4 2697A), we get to about 80Gb/s with CPU maxed contending for the vm page free lock when maxcache is 0. When it is set to 0x60000 we reach 95Gb/s with idle CPU.

We currently set the maxcache to 0 on the pgcache uma zone. Under a heavy Netflix ktls encrypted web workload, this leads to lock contention on the vm page free queue from vm_page_zone_import / vm_page_zone_release as the buckets are frequently drained. This change adds a tunable to allow the administrator to specify the maxache. On a Netflix 100G cache (16 core / 32t Xeon E5-v4 2697A), we get to about 80Gb/s with CPU maxed contending for the vm page free lock when maxcache is 0. When it is set to 0x60000 we reach 95Gb/s with idle CPU.