This read-only integer reports the total amount of memory in the 'low' memory region, the portion the kernel can address directly and where all kernel data structures must reside. An admin watches this because exhaustion of low memory specifically, even with plenty of high memory free, can still cause kernel-level allocation failures. For example, an admin seeing kernel allocation warnings despite plenty of free RAM overall would check this low-memory-specific object to confirm the low region itself is under pressure.