This read-only integer reports the total amount of memory in the 'high' memory region, defined as all physical RAM above roughly 860MB that the Linux kernel accesses only through indirect tricks and which can hold data cache. An admin on older 32-bit systems checks this to understand how much of installed RAM falls into the kernel's high-memory region versus directly addressable low memory. For example, an admin diagnosing memory-pressure symptoms on a 32-bit Linux server with several gigabytes of RAM would look at this object to see how much memory is only reachable via the more expensive high-memory access path.