GH_RSRVPGCNT is a system parameter that specifies the number of pages in the resident image code granularity hint region that the Install utility can use after the system has finished booting.
If bit 2 of the LOAD_SYS_IMAGES parameter is set, the image LDR$WRAPUP releases all unused pages in the granularity hint region at the the end of system startup. The unused pages of the resident image granularity hint region are either reserved for future use, or given back to the free memory list.
GH_RSRVPGCNT specifies the number of pages that LDR$WRAPUP attempts to leave in the resident image code granularity hint region. If the GH_RSRVPGCNT number of pages is larger than the unused pages in the granularity hint region, the region is not expanded to accommodate the number of pages requested.