This is the fraction of pages in each zone that are can be stored to per-cpu page lists. It is an upper boundary that is divided depending on the number of online CPUs. The min value for this is 8 which means that we do not allow more than 1/8th of pages in each zone to be stored on per-cpu page lists. This entry only changes the value of hot per-cpu page lists. A user can specify a number like 100 to allocate 1/100th of each zone between per-cpu lists.
The batch value of each per-cpu page list remains the same regardless of the value of the high fraction so allocation latencies are unaffected.
The initial value is zero. Kernel uses this value to set the high pcp->high mark based on the low watermark for the zone and the number of local online CPUs. If the user writes ‘0’ to this sysctl, it will revert to this default behavior.