This is the fraction of pages at most (high mark pcp->high) in each zone that are allocated for each per cpu page list. The min value for this is 8. It means that we don't allow more than 1/8th of pages in each zone to be allocated in any single per_cpu_pagelist. This entry only changes the value of hot per cpu pagelists. User can specify a number like 100 to allocate 1/100th of each zone to each per cpu page list.
The batch value of each per cpu pagelist is also updated as a result. It is set to pcp->high / 4. The upper limit of batch is (PAGE_SHIFT * 8).
The initial value is zero. Kernel does not use this value at boot time to set the high water marks for each per cpu page list.